AADSTS16000 — personal account not in 'Microsoft Services' tenant, cannot access the Azure support portal at all

I'm locked out of Azure support entirely and looking for a way to reach support.

The error (when signing into the Azure support portal):

interaction_required: AADSTS16000: User account '{EUII Hidden}' from identity provider 'live.com' does not exist in tenant 'Microsoft Services' and cannot access the application 'Microsoft_Azure_SupportPortalExtension' in that tenant. The account needs to be added as an external user in the tenant first.

Background:

• My Microsoft account was removed from its Entra tenant (Tenant ID: 312545fa-193d-4d43-8e8c-67abd8f82201). I did not remove it myself.
• The Azure portal fails the same way — I cannot view, manage, or cancel my subscription, yet I'm billed about $82/month.

What I've tried:

• support.microsoft.com — unable to complete filing a new support request.
• Azure Commercial Support phone (+1-800-865-9408) — could not reach a human through the IVR.
• Previous Service Request 7109471075 (opened Sept 28 via chat) — appears closed without resolution.

My question: How can I get support when the support portal itself rejects my sign-in? Is there a way to be added as an external user to the 'Microsoft Services' tenant, or is there an alternative channel (email, chat link, etc.) to file a billing support request without going through the portal?

Happy to verify my identity via private message. Thank you.