Subject: Error 399287 – Global Administrator locked out – SMS MFA blocked

Dear Joris Birnie,

First of all, if there is another Global Administrator who can access the tenant, that person can reset your authentication methods, allowing you to register a new phone and set up alternative ways to access your account. For more information and instructions, please ask the other IT administrator to follow the official Microsoft guide available here: Manage authentication methods for Microsoft Entra multi-factor authentication - Microsoft Entra ID | Microsoft Learn.

However, if you are the only admin, only Microsoft Support's Data Protection team can assist with account ownership verification and administrator recovery. I recommend contacting Microsoft Support and specifically requesting escalation to the Data Protection / Account Recovery team for a Global Administrator lockout.

As a forum member like you, I do not have access to internal Microsoft systems or any special escalation channels. The suggestions I provided are based on what I have observed from many similar cases I have seen in the forum community.

Option 1: Try to contact Microsoft Data Protection Support by phone (Primary Method)  

The most direct method is to call Microsoft's support line to raise a request for resetting your authentication method and regaining your account access. For a full list of regional numbers, you can also visit this official page: Customer service phone numbers - Microsoft Support. The support team will assist you as soon as possible. For reference:  Get support | Microsoft Docs   

Note: You may also consider calling a Microsoft support number for a different region if support in your local region is unavailable or unable to route your case appropriately.

(While calling, you may hear an introduction of about 30 seconds such as "you can visit the link...". You can ignore it and wait until you are presented with the options. Then press "1" as a business email user, and again "1" for technical help.)     

Here are some tips and an example of a prompt to help you navigate the IVR more effectively: 

In some countries, it is an automated conversation like: First, when you call the hotline, it will be asked as follows: 

IVR: What kind of problem are you concerned about? 

You: Authenticator. 

IVR: What kind of product do you use? 

You: Office 365 for business. 

IVR confirmation: education or company account? 

You: For companies 

IVR: Are you an administrator? 

You: Yes. 

IVR: Do you have the other administrator in your organization? 

You: No. 

IVR: Do you need a... Service request? 

You: Yes  

This process should connect you with a live agent who will create a service request with the Data Protection team. They will then contact you to help you regain access. 

Option 2: Create a Temporary Account (Trial Tenant) to Submit a Support Ticket (Alternative Method) 

If the automated phone system does not get you to a human agent, one workaround is to create a separate trial Microsoft 365 tenant and use that tenant to open a support ticket on behalf of the locked tenant.

• Sign up for a new Microsoft 365 Business trial using this link: Compare All Microsoft 365 Plans. You will need to use a different, personal email address to register. 
• Once the trial account is created, log in to its Admin Center > From the Admin Center, open a new Service Request. For reference:  Get support | Microsoft Docs   
• In the ticket description, explain that you are locked out of your primary tenant (your.onmicrosoft.com) and that you need to speak with the Data Protection team to regain access.
• Remember to provide your locked account's details and a good contact number for them to reach you. 

Important:

- Please remember to cancel the trial subscription after your original account issue is resolved to avoid any future charges. 

- When creating the support request, I also recommend disabling or bypassing the AI/Support Assistant option if presented and choosing the path that allows you to contact a support engineer directly.

Thank you for your patience and understanding. If you have any questions or are stuck on any steps, please feel free to reach out. I'm looking forward to your update.