Dear @maribel999,
thank you for sharing your question with the Wefugees Community.
If the GU is managed by a private or none state organization or company, you can complain about the GU Manager both to his/her head of department/organization and to the German relevant authority, which has given the contract to this organization or company. This German authority could be, for example, Social Welfare Office (Sozialamt) or Foreigners Office (Ausländerbehörde). However, if the GU is managed by the employees of a state authority, such as by the employees of Social Welfare Office or Ausländerbehörde, you can complain about the GU Manager to his head of department/Office in Social Welfare Office or in Foreigners Office.
If you need help in writing the complaint, a migration counseling office such as, DRK/BRK, Diakonie, AWO or Caritas, can help you with it, free of charge.
I hope, you have got your answer. I am a MBEON consultant. If you wish to contact me directly, you can see my profile and follow the instructions there.
Best wishes
Fardeen Noori