Dear Kathrin Rüppel,
We apologize for all the trouble caused by this issue.
Do you have a Microsoft 365 Business account? If yes, you can contact Microsoft Phone Support Get support - Microsoft 365 admin | Microsoft Learn
Or if you have a personal Microsoft account, you can talk to a support agent by simply describing the issue on this page Contact - Microsoft Support, then click Get Help, click 'Contact Support' on the bottom, choose Products and services(Microsoft 365 and Office), choose Category(Technical Support), click Confirm, then you will get a link to chat with a support agent.


Appreciate your patience and understanding and thank you for your time and cooperation.
Sincerely,
Tina | Microsoft Community Moderator