I cant sign in Outlook and Teams due to MFA loop

Dear Thommy Fang,

I'm sorry to hear you're unable to access Outlook and Teams after losing the phone that was registered with Microsoft Authenticator.

If this is an education account, please contact your University's IT Help Desk or Microsoft 365 administrator and ask them to reset your MFA registration and remove the lost Authenticator device from your account, this will allow you to reconfigure MFA from scratch on your new device. As a forum user, I do not have administrative access to change these settings. Only your IT team has the ability to adjust or reset your MFA configuration. You can also refer to this Microsoft support article for more information: Manage authentication methods - Microsoft Entra ID | Microsoft Learn  

In case you are the only Global Administrator and you are completely locked out from the tenant. You might need to contact Microsoft Support team 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.   

To help you navigate the automated phone system (IVR), here's an example of what the conversation might look like:

IVR: What kind of problem are you worried about?

You: Admin account locked

IVR: What kind of product do you use?

You: Office 365 for education

IVR: Does it count for education or business?

You: For education

IVR: Are you an admin?

You: Yes

IVR: Do you have another administrator in your organization?

You: No

IVR: Need a service request?

You: Yes

This should help you connect with a live support agent who can help you directly.

If you can't create a support ticket during the call, I recommend creating a temporary tenant account and submitting the support request from there. To create a new tenant, follow these steps:

1. Visit Office 365 E3 - Enterprise Collaboration and Productivity | Microsoft    
2. Select any plan and click Try for free.    
3. Complete the setup to create a new tenant.    
4. Ticket support: In the Microsoft 365 admin center>support>help & support. You can create a support ticket: https://admin.microsoft.com/#/support/requests     

Important: Please remember to cancel the trial subscription once your issue is resolved to avoid any charges.

I understand that this issue may take some time to resolve and could impact your workflow. However, the following solutions have been effective in resolving Microsoft Authenticator issues.

If you have any other questions, please feel free to reach out.

If the answer is helpful, please click "Yes". If you have extra questions about this answer, please click "Comment".   

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