Error Code: 399287 MFA via SMS not working

Please understand that as forum moderators, we do not have the tools or sufficient access to make changes to user accounts, including logging in, resetting passwords, or modifying access rights. For your security, only Microsoft Support can assist with these requests. However, I will do my best to guide you using publicly available documentation, research, and community experience.  

Hello @Vithusha T,

Welcome to Microsoft Q&A Forum!  

To better understand your situation and guide you correctly, could you please confirm whether you are an end user or a global administrator of your Microsoft 365 tenant?  

The next steps will depend on your role:  

1. If you are an end user  

The quickest and most effective solution is to contact your organization’s IT administrator. They can revoke your current Multi‑Factor Authentication (MFA) settings and allow you to re‑register.   

You may share this official Microsoft article with them for detailed guidance: Manage authentication methods for Microsoft Entra multifactor authentication - Microsoft Entra ID |…    

2. If you are an administrator  

Please check whether there is another admin in your tenant. If so, they can reset your MFA configuration by:  

• Signing in to the Microsoft Entra Admin Center  
• Navigating to Users > Your Account > Authentication methods  
• Selecting Require re‑register MFA  

You will then be prompted to set up MFA again at your next login.  

3. If you are the only administrator  

In this case, you will need to contact Microsoft’s Data Protection team, who are authorized to verify your identity and reset MFA settings. Please call Microsoft Support using the appropriate regional hotline listed here: Customer service phone numbers - Microsoft Support  

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

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

In some regions, the initial interaction may be automated, so here’s a general idea of how the conversation might go to help you prepare:       

• What kind of problem are you experiencing?          
• Answer: Authenticator          
• What products do you use?          
• Answer: Office 365 for business          
• Is this for an education or company account?          
• Answer: For companies          
• Are you an administrator?          
• Answer: Yes          
• Are there any other administrators in your organization?          
• Answer: No. I am the only admin in my tenant           
• Do you need a... Service request?           
• Answer: Yes. I need to create a ticket. Please send me direct to the Data Protection Teams.       

During the phone call, you will need to provide the information associated with your subscription, such as your company name, billing details, phone number, and an alternate email address, etc. This information allows the Data Protection team to verify your identity and securely assist you in regaining access to your administrator account.      

Could you please confirm which of the three cases applies to you? Once I have this information, I can guide you further and ensure you get the correct next steps.  

Thank you, and I look forward to your reply. 

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.