Azure: The sign-in stops at the MFA step

Hello,

I changed my phone and can no longer sign in to the Azure portal or the Microsoft Entra admin center. The sign-in stops at the MFA step: the page shows the number to approve, but no request reaches the Microsoft Authenticator app, and the app shows an 8-digit code while the tenant asks for 6.

My personal Microsoft account works normally (I can sign in to account.microsoft.com and manage its verification methods), so the issue is only the tenant's MFA. (Also az login from powershell is ok).

I am the only user and Global Administrator of the tenant, so no other admin can reset my authentication methods. How reset my MFA, or allow me to re-register it.