Locked Out of Admin Account — MFA reset needed

You will have to contact Microsoft business support. I think the data protection team will be able to assist you with this.

Hi @怡禎 胡
Thank you for reaching out to the Microsoft Q&A Forum, and I apologize for any inconvenience this issue has caused. 

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According to your situation, since you are the only Global Administrator and you are completely locked out from the tenant. So, only Microsoft Support team can help you in this MFA issue. You might need to contact us via phone service number: Customer service phone numbers - Microsoft Support. The agent will be able to create a ticket for you under the affected tenant and then transfer this ticket to Data Protection team who could help you to regain access.  

Please note that this team is always overwhelmed, so you might need to wait for them to call you, this should take 3-10 working days. I know that this is not a convenient solution to hear but it seems to be the only way, and it's recommended that you should have a secondary/backup Global Administrator to fix this issue on your own.   

In case the phone line is not supportive, you can consider directly submitting a support request as a helpful workaround:   

-Create a temporary Microsoft 365 tenant using a trial license: Go to Microsoft 365 Business Plans and Pricing and click Try for free to set up a temporary Microsoft 365 tenant with a trial license.

-Use this new account to sign in to the Microsoft 365 Admin Center and submit a support request on behalf of your primary (locked) account.  

-Click Help & Support > then choose Create a support request.

Note: This method doesn't require you to use your new account for your business. Instead, it allows you to create a temporary global administrator account so you can submit a support request, as your original global administrator account is locked out due to issues with multi-factor authentication. The trial account is free for one month. Be sure to delete it after submitting your support request to avoid any automatic renewals or charges from Microsoft.    

For further instructions, you can follow this guide: Get support - Microsoft 365 admin | Microsoft Learn  

I hope for your understanding and patience in this matter, as I really want to help you. However, this issue is beyond my control because I’m limited in my forum moderator role and cannot access internal databases or escalate cases to the Microsoft Support team (Data Protection Team) directly. Therefore, please kindly reach out to them for the most efficient help.  

Wish you a pleasant day!

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