Only Global Administrator locked out of Azure / Entra ID due to inaccessible MFA phone number

I am unable to sign in to the Azure Portal because Microsoft Entra ID is requiring MFA verification using an old phone number that I can no longer access.

The account I use is a Microsoft personal account registered with a custom domain email address.

I can successfully sign in to my Microsoft account at account.microsoft.com using my password, and no SMS verification is required there.

However, when I try to access the Azure Portal, I am prompted to verify my identity. The only available verification methods are:

• Send an SMS to the registered phone number
• Call the registered phone number

Both methods use the same old phone number, which is no longer available. I also do not see any option to use Microsoft Authenticator or another authentication method.

I tried to create a support request from the Azure Portal under "Microsoft Entra Directories, Domains, and Objects", but my subscription is currently on the Basic support plan, so I cannot create a technical support request.

How can I reset the MFA / authentication methods registered in Microsoft Entra ID so that I can register a new phone number or Microsoft Authenticator?

Because I cannot complete MFA, I am unable to access the Azure Portal and cannot update the authentication methods myself.

If this requires tenant recovery or escalation to the Data Protection Team, please let me know how I should proceed.

I can provide the Tenant ID, Subscription ID, account information, domain ownership verification, billing information, or any other required proof of ownership through a private method if necessary.

There is no other Global Administrator in the tenant who can reset my MFA methods.

Thank you.