Singen

Dipl. Wirt.-Ing. Martin Klumpp

Certified Public Accountant / Tax Consultant / Managing Director / Partner / Team Leader

Martin Klumpp is a partner and managing director of Trewitax Deutschland GmbH and has been with the company since 1996. With many years of experience as an auditor and tax consultant, he serves our clients with his expert knowledge in the areas of international tax consulting, tax structure and structuring consulting, financial consulting, data protection and restructuring consulting. His further area of expertise is tax advice for insolvency mandates. Until 2018, Martin Klumpp was a lecturer at the Duale Hochschule BW Villingen-Schwenningen in the area of tax and business. He is also a regular speaker for DATEV in the area of digital law firms.

Dipl. Wirt.-Ing. Frank Riedel

Certified Public Accountant / Tax Consultant / Specialist Consultant for International Tax Law / Managing Director / Partner / Team Leader

Frank Riedel is a partner and managing director of Trewitax Deutschland GmbH and has been with the company since 2003. Prior to that, he worked as a manager of an international auditing and tax consulting firm. As an experienced auditor, tax advisor and specialist consultant for international tax law, he supports our clients in the areas of international tax consulting, tax structure and structuring consulting, voluntary and legally required audits, international accounting and group accounting.

Dr. Olesja Dittmann

Certified Public Accountant / Tax Advisor / Specialist Advisor for International Tax Law / Managing Director / Partner / Team Leader

Dr. Olesja Dittmann is a partner and managing director of Trewitax Deutschland GmbH since 2019. She has been working for Trewitax as a tax consultant, auditor, specialist consultant for international tax law and authorized signatory since January 2014.

She serves our clients in the main areas of ongoing tax and business consulting, auditing, M & A and international tax consulting. With the foreign languages English, Russian and Spanish, she has comprehensive language skills for international tax consulting.

Her further area of expertise is tax advice on insolvency mandates.

Ansgar Woltemate

Certified Public Accountant / Tax Consultant / Managing Director / Partner / Team Leader

Ansgar Woltemate is a partner and managing director of Trewitax Deutschland GmbH and continues to work as an auditor and tax consultant. Since 2013, he has been supporting our clients in the main areas of ongoing tax and business consulting (esp. of corporations), auditing and M&A projects.

His further areas of expertise are tax advice to employees in cross-border matters (in particular to Switzerland) and the support of clients with project company structures (e.g. property developers).

Julia Woltemate

Certified public accountant / tax consultant / authorized signatory

Julia Woltemate has been working for Trewitax Deutschland GmbH as an auditor and tax consultant since 2021. Prior to that, she worked as a manager at an international auditing and tax consulting firm in the Financial Services division.

As an experienced auditor and tax advisor, Julia Woltemate supports our clients in the main areas of international tax consulting, tax structure and structuring consulting as well as M&A.

She has extensive knowledge and many years of practical experience in group accounting, international financial reporting (IFRS) and annual auditing.

Antje Deichmeier

Tax consultant / authorized signatory / team leader

As a tax consultant and authorized signatory, Antje Deichmeier supports our clients in the main areas of preparing annual financial statements and tax returns, international employee taxation, optimizing financial accounting and ongoing tax consulting.

Her other areas of expertise include the preparation of insolvency accounts and tax advice to insolvency clients.

Stefan Mayer

Tax consultant / authorized signatory / branch manager Constance

Stefan Mayer works for Trewitax as a tax consultant and authorized signatory. Since 2010, he has been supporting our clients in the main areas of ongoing tax and business consulting, the preparation of annual financial statements and tax returns.

He also serves as the audit manager for voluntary and statutory annual audits.

Tatjana Golowatisch

Tax consultant

Tatjana Golowatisch has been working for Trewitax GmbH as a tax consultant since April 2017. She supports our clients in the main areas of ongoing tax advice, in particular for corporations in national and cross-border matters, as well as in the preparation of annual financial statements and tax returns.

In addition, Julia Golowatisch advises our clients on international tax law and M&A projects. With the foreign languages Russian and English, she has comprehensive language skills for international tax consulting.

Robert Stoll

Steuerberater

Julian Rottach

Lawyer

Julian Rottach joined Trewitax GmbH as a lawyer after studying law with a focus on commercial criminal law. He is a graduate of a specialist course in tax law and advises our clients on the interface between law and taxes.

His consulting focus is on corporate and private succession planning. In addition, he regularly assists our clients in connection with the formation, restructuring and liquidation of partnerships and corporations.

As in-house lawyer of Trewitax GmbH, Julian Rottach also represents the legal interests of the company and advises management and colleagues on legal issues.

Petra Baumann

Attorney at Law

Melina Heiser

Office Manager / Bachelor of Arts / Data Protection Officer / Team Leader

Melina Heiser has been a part of the Trewitax team since 2016. She leads the office management and is responsible for the support of clients and internal processes. Since 2018 she is also still working as a data protection officer.

Rigona Asaj

Stud. Bachelor of Law – Wirtschaftsrecht

Mikail Ates

Auszubildender zum Steuerfachangestellten

Nathalie Bahmüller

Steuerfachangestellte

Dennis Balemans

IT-Consultant

Brigitte Brütsch

HR-Managerin

Antonio Celano

Assistant tax consultant / Stud. Bachelor of Arts - Taxes and Auditing

Stefanie Dering

Office Manager

Chantal Buhl

Office Manager

Katharina Dietrich

Office Manager

Katharina Dietrich is a trained businesswoman for tourism and leisure. After 13 years, she made a change in industry and has been working as Office Manager for Trewitax GmbH in Singen since April 2021.

The day-to-day, smooth management of the office and client care are among her responsibilities.

Aynur Dogan

Steuerfachangestellte

Aynur Dogan hat im Juli 2022 ihre Ausbildung zur Steuerfachangestellten erfolgreich abgeschlossen. Seit August 2024 verstärkt sie das Team der Trewitax in Freiburg und betreut Mandanten in den Bereichen der Finanzbuchhaltung und Lohnabrechnung sowie bei der Erstellung von Jahresabschlüssen und Steuererklärungen.

Anja Ehinger

Office Manager

Maximilian Ehni

Steuerfachangestellter

Kim Fischer

Werkstudentin

Kim Fischer studiert Betriebswirtschaftslehre im Bachelorstudiengang und ist als Werkstudentin im Bereich der Jahresabschlussprüfungen, Finanzbuchhaltungen und Einkommensteuererklärungen für die Trewitax tätig. 

Venera Gajtani

Steuerfachangestellte

Venera Gajtani absolvierte im Juli 2022 erfolgreich Ihre Ausbildung zur Steuerfachangestellten. Seit Dezember 2024 ist sie Teil des Teams der Trewitax in Freiburg und unterstützt unsere Mandanten in den Bereichen Finanzbuchführung, Erstellung von Jahresabschlüssen und Steuererklärungen.

Elias Fogarizzu

Stud. Bachelor of Arts – Steuern und Prüfungswesen

Elias Fogarizzu arbeitet seit August 2025 für die Trewitax GmbH. Er absolviert gerade das duale Studium für Steuern und Prüfungswesen an der DHBW Villingen-Schwenningen.

Jana Haberstroh

Assistentin in der Steuerberatung und Wirtschaftsprüfung / Bachelor of Arts – Steuern und Prüfungswesen

Lena Hauke

Stud. Bachelor of Arts - Taxation and Auditing

Tim Heine

Stud. Bachelor of Arts - Business Informatics

Christine Krug

Tax specialist

Lina Klumpp

Auszubildende zur Steuerfachangestellten

Nach dem Abschließen ihrer allgemeinen Hochschulreife hat Lina Klumpp im September 2023 ihre Ausbildung zur Steuerfachangestellten bei der Trewitax GmbH begonnen. In den ersten drei Monaten unterstützt sie das Office und danach durchläuft sie die weiteren Bereiche der Ausbildung zur Steuerfachangestellten.

Pankaj Kumar

Assistent in der Steuerberatung und Wirtschaftsprüfung

Joanna Nocon

Tax assistant / Wage and salary specialist / Team leader

Joanna Nocon has been working for Trewitax GmbH since 2013 as a tax clerk and payroll assistant. As team leader, she is responsible for the payroll department and her areas of expertise include consulting, optimization and preparation of payrolls. She supports our international clients in the registration and payment of German social security and payroll taxes.

As an experienced tax specialist, Joanna Nocon assists our clients in setting up, digitizing as well as optimizing their financial accounting.

Martina Osswald

Accountant

Luisa Pankraz

Assistant tax consultant

Stefanie Pfaff

Steuerfachangestellte / Lohnbuchhalterin

Daniel Tessendorf

Assistant in tax consultancy and auditing / Business economist GA

Xenia Windt

Assistent in der Steuerberatung und Wirtschaftsprüfung / Bachelor of Arts – Steuern und Prüfungswesen

Tijana Vasiljevic

Stud. Bachelor of Arts – Digital Businessmanagement

Tijana Vasiljevic ist seit September 2023 bei der Trewitax GmbH tätig. Gleichzeitig absolviert Sie ihr Studium zum Bachelor of Arts im Bereich "Digital Business Management" an der DHBW in Villingen-Schwenningen.

Moira Vodopivec

Assistentin in der Lohnbuchhaltung