Hi @Si ,
Unfortunately no there is no other way to restore the access, I will suggest you to phone the support desk get-help-support and please keep the proof of ownership of the business that was shared with Microsoft at the time of signing up . Due to security reasons the Office 365 team would require to verify your identity with the information they would have about you before they can help you further.
Hope the information is helpful and it helps you obtain access to your Office 365 tenant as global admin .
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