Error Code 399287, unable to log in it to admin account

Hi @Kostrej,

Welcome to Microsoft Q&A forum.

Thank you for contacting us regarding the issue you're experiencing with your account sign in.

When multi-factor authentication (MFA) is enabled, signing into the account requires both the password and a secondary verification method such as the Microsoft Authenticator app or a registered phone number. If access to this second factor is lost (for example, due to a device change or number update), the system will restrict access to safeguard the account against unauthorized use.

Based on your description, it appears that you are the sole admin in your company. In this case, please find below the steps to recover your account:

1/ Sign in using alternate verification method:

Try to log in at https://office.com, click on the "Sign-in options".

If your phone number was previously registered to your account, you may be able to choose to receive a verification code via SMS or phone call instead of entering your password.

Notes:

If you don't see the Sign in another way link, it means that you haven't set up any other verification methods and that you'll have to contact the Data Protection team for assistance to recover your account. 

2/ Contact Microsoft Support via phone:

If you have only one administrator account on your system and it's locked, you'll need to contact the Microsoft Data Protection team by phone. You can find the support number for your region here: Customer service phone numbers - Microsoft Support

In this situation, only the Microsoft Data Protection team has the necessary privileges to reset your account at the server level. They are the only team authorized to handle issues related to access recovery and account security.

Please note that forum moderators do not have access to user account settings and cannot assist with logging in, resetting passwords, or changing access rights. While we do not have access to internal systems or administrative tools required to resolve account-specific or backend-related issues, we’ll continue doing our best to support you within the scope of our responsibilities. 

During the call, you will be required to provide information related to your subscription, such as:

• Name of your organization
• Payment Information
• Registered phone number
• Alternate email address

Once your identity is verified, the privacy team will be able to reset your MFA settings. You can then reset your account in the Microsoft Authenticator app on your new device or choose a different authentication method to sign in.

Tips for navigating the IVR:

In some countries, an automated voice system is used. Example of a dialogue:

• IVR: What problem is bothering you?
• Client: Lost access to the only admin account
• IVR: What product do you use?
• Customer: Office 365 for business
• IVR: School or Business Account?
• Client: Companies
• IVR: Are you an administrator?
• Client: Yes
• IVR: Is there another administrator in your organization?
• Client: No. I am the only admin in my tenant    
• IVR: Do you need to create a support ticket?
• Client: Yes. I need to create a ticket. Please send me directly to the Data Protection Teams.

3/ Create a new additional trial tenant:

In case you are unable to contact the frontline support:

Consider signing up for a trial subscription to create a new tenant. After the set up, you can access the new tenant's admin console and submit a support ticket to speak with the data protection team on behalf of the previous tenant. Once your issue is resolved, please remember to cancel the trial subscription to avoid any unintended charges.

If your organization's subscription is from a partner or reseller:

Contact the reseller support provider to help open a service request on behalf of you.

Hopefully, this information will help you successfully contact the Microsoft Data Protection team and open a support request. I sincerely hope that my answer comes on time, and you are doing well.

Thank you for your patience and your understanding during this process. If you have any questions, please feel free to reach out.

I'm looking forward to your reply.

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