Tenant lockouts can occur when all Global Administrators lose access due to misconfigured policies, expired credentials, or MFA failures.
For any scenarios that involve Customer tenant lockout, Microsoft must work directly with a Global Administrator of the tenant where access issues are occurring.
End customers should always try recovering access through the Self Service Password Reset tool before contacting Microsoft for support.
To contact Microsoft Support: Find Microsoft 365 for business support phone numbers by country or region.
Reference: Preventing Tenant Lockouts - Partner Center | Microsoft Learn