Only phone support can fix it. They will need to prove you control the domain and then can release it or help you get into the account.
Support information:
You will need to contact the Microsoft Data Protection team for assistance with this issue. The Data Protection team is specifically equipped to handle these matters, verify the required information, and take the appropriate action to resolve your issue.
Call during your country's business hours. If you get the phone bot (and not immediately told to use the admin portal) make sure you ask for the data protection team and say "I cannot access admin center and I am the only admin user".