error 500121 - Authenticator App and new iPhone

Colette Acker 0 Reputation points
2026-09-15T14:19:19.36+00:00

I haven't been able to access Office 365 in 5 days!!! I have a case number and no one is calling me!!!!

I am the Global Administrator for a Microsoft 365 business tenant. I got a new iPhone, and my Microsoft Authenticator registration is still associated with my old iPhone. I cannot access the old phone because its display is broken. I am completely locked out of my administrator account and receive error 500121. I need a tenant recovery/Data Protection case to reset the MFA registration for my Global Administrator account.

There are 3 other global administrators and none of their authenticator apps are working either!

Microsoft 365 and Office | Subscription, account, billing | For business | Other
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  1. Killian N 4,145 Reputation points Independent Advisor
    2026-09-15T14:50:37.5+00:00

    Hi Colette,

    From what you've described, it sounds like your Multi-Factor Authentication (MFA) setup may need to be reset. This can sometimes happen after switching to a new device, replacing a phone, or reinstalling the Microsoft Authenticator app. Since your new device hasn't been registered yet, the authentication requests may still be linked to your previous device, which can leave you stuck in a sign-in loop. 

    If you are the only admin and have already created a ticket, please wait for the Data Protection Team to contact you. They may currently be handling a high volume of cases, which could be causing a delay.  In the meantime, you can provide the following information via email to the agent who is handling your case and ask them to assist you further: 

    • Tenant ID: 
    • Email address: 
    • Screenshot or copy of the most recent invoice: 
    • Phone number: 
    • Available time for contact: 
    • TXT record: 

    Please send these details to the agent and request their assistance in expediting the review of your case. 

    Once your Global Administrator has successfully regained access, you will be able to manage and reset the MFA methods for the other affected administrator accounts through the Microsoft Entra admin center. This is usually the quickest way to regain access. 

    For reference: Manage authentication methods for Microsoft Entra multifactor authentication - Microsoft Entra ID | … 

    I hope this helps point you in the right direction. If you have any updates or additional questions, feel free to reply back and I'll do my best to assist further. 

    Best regards, 

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