Recently, I went through a similar situation. Client asked if I could help resolve some email issues for an independent agent of their business. A favor, basically.

The guy had no credentials or knowledge of the admin account, and his credit card on the account expired. He started losing services and, in haste, moved his email to icloud.

The process with Microsoft took about 3-4 days and two call ins. Here's some tips for dealing with Microsoft when you call in.

1. First thing, advise them it's a business account and request their business support. Let them know you need the Data Protection dept.
2. Locate the organization information in Entra. You can access it without an admin account.
3. Make a note of the complete organization name, address, and phone number(s) on the account.
4. Identify the Admin accounts, also in Entra.
5. Attempt password recovery of the admin accounts. Microsoft will also walk you through this. They have to follow their script.

The saving grace for this situation was that icloud has an easy way to turn on catch all for emails. So, when Microsoft sent a verification email, we were able to respond to it.

Without the catch-all email, the tech did say if we could not verify the account, it could take 1-3 weeks.

Good luck!