I'm sorry that you have had such experience with Microsoft support.
Unfortunately, only the support can help you with this case because MFA will be required for all the actions you listed in your request.
Please, try opening a new case using Microsoft Entra or Azure Portal and follow the steps below. You can open the case from the Tenant that you have access to, but it would be good to have the affected tenant name or its Tenant ID. Your case will be handled by someone from the identity team. Explain the engineer what your issue is but let him know that you are on a Tenant Lockout scenario. The engineer will validate whether or not you are the only GA on that domain and will help you accordingly.
- Sign in to the Microsoft Entra admin center as at least a Service Support Administrator.
- Browse to Learn & support > New support request.
- Follow the prompts to provide us with information about the problem you're having.
Thanks,
Fabio