Hi Dave Brayley
Thank you for posting your question in the Microsoft Q&A forum.
Since you are the only Global Administrator and you suddenly locked out of the Admin Center, you must contact Microsoft Telephone Support directly to reach the Data Protection Team. They are the only support tier authorized to verify your identity over the phone and unlock your tenant.
- Locate your local support number here: Customer service phone numbers - Microsoft Support and call the number for your region (do not request "Technical Support" Request assistance with an "Admin Account Lockout" or "Data Protection")
- You will be required to provide documentation proving you own the business (business registration, tax documents, and proof of domain ownership) to have the Global Admin settings reset or transferred to you.
Please note that this team is always overwhelmed and has a strict verification process, so you might need to wait for them to call you, this should take 7-14 working days.
Additionally, please note that for security reasons and this forum is a peer-to-peer community, so members can share advice and experiences only.
I hope this information proves useful to you.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.