Hello @Phil Brownsord,
Thank you for posting your query on Microsoft Q&A.
As we discussed over email, this issue relates to a tenant lockout situation where no other global admin in the tenant has the necessary admin rights to re-register MFA.
To resolve this, we engaged our Data Protection team through a support ticket. Please connect with our support team via the ticket, and they will assist you in resolving the issue.
I hope this information is helpful. Please feel free to reach out if you have any further questions.
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