Sole Global Admin locked out - lost MFA device, SSPR phone verification returns error

I believe yes, you are required to contact the Microsoft support team and request escalation to Data Protection for MFA reset and tenant access restoration.

https://support.microsoft.com/en-us/support/

J'ai le même problème actuellement. 

Update: RESOLVED. Posting the full path in case it helps someone else in the

same situation.

Summary: sole Global Administrator, cloud-only tenant, Authenticator device

physically destroyed, authentication methods list empty, SSPR second step failing.

Resolved in about 24 hours through the Microsoft 365 Data Protection team.

WHAT ACTUALLY WORKED

1. Reaching a human. With no admin access there is no way to open a support case.

I created a separate free trial tenant, and from its admin center I opened a

support request describing the problem with the ORIGINAL tenant. That was the

only way in. (I cancelled the trial afterwards so it would not bill.)

2. The first agent routed the case to the Data Protection team, and an engineer

took ownership the same day.

3. Identity verification was done by phone. The engineer called the phone number

already registered on the tenant profile - in our case the company director's

number - and the director then added me to the call. We confirmed full name,

both contact phone numbers, and both e-mail addresses on record.

4. Approval step. I received an e-mail titled "MFA reset request for the GA/CA

account" and replied with the exact sentence "I approve this request".

5. The reset was executed shortly after. I signed in at portal.office.com with

the EXISTING password (it was never the problem), and instead of the

Authenticator prompt I got the "More information required" registration wizard.

Scanned the QR with Authenticator on the new phone. Access restored.

PRACTICAL NOTES THAT COST ME TIME

- The engineer's e-mails went to the case contact address, which was the

.onmicrosoft.com mailbox of the trial tenant, not my normal inbox. I did not see

them for hours. Tell the engineer explicitly which mailbox you can actually read,

and check the trial tenant's Outlook.

- Some of the case correspondence CC'd the locked account itself. State clearly and

repeatedly that you cannot read that mailbox - it is the one you are trying to

recover.

- Keep the TrackingID in the subject line and always reply in the same thread.

My first case was closed as a duplicate and a new ID was issued; replying to the

closed one would have gone nowhere.

- Prepare identity evidence before the call: tenant ID, user unique ID,

subscription order number, invoice number, company registration and VAT number,

billing e-mail. Having it ready made the verification call short.

- Do NOT revoke sessions. That is what killed my own remaining admin session and

turned an inconvenience into a full lockout.

AFTER RECOVERY

Registering a second method was not straightforward - phone/SMS registration

returned "We ran into a problem" every time, which matches the current retirement

of Microsoft-provided SMS and voice authentication. Passkeys and a second

Authenticator instance are the way forward.

What I am doing now, and what I would recommend to anyone reading this:

- more than one authentication method on the admin account, on more than one device

- a second, cloud-only break-glass Global Administrator account

- a custom domain added to the tenant, so ownership can be proven by DNS TXT

instead of documents and phone calls

Thanks Jamony - your answer was correct: there is no client-side bypass, and the

support route through the organization's registered contact details is the only

one that works.

You lost the usable MFA registration, revoked the remaining admin session, and SSPR cannot complete its second verification. There is no safe client-side bypass; recovery now requires an authenticated administrator or Microsoft verification. Stop repeated sign-in and reset attempts to avoid adding lockout signals. Contact Microsoft 365 business support using the organization’s registered contact details; Microsoft may verify the request through data stored in the tenant profile. If the subscription was bought through a partner, contact that partner because it owns the support route. Keep the tenant ID, custom domain, subscription or order number, billing records, and registered-contact access ready, but share them only in the support case. Ask for tenant administrator access recovery, not a public forum reset. After access is restored, create two cloud-only emergency Global Administrator accounts, register independent phishing-resistant credentials, monitor their use, and test them regularly so one lost device cannot lock the tenant again.