Hello Rui Mateus1,
Thank you for posting in the Microsoft Community.
I understand you're unable to access the Microsoft account due to Multifactor authentication (MFA).
If you are end user or have another global administrator available, they can assist you in resetting your user/admin password and MFA. For more information, Manage authentication methods for Microsoft Entra multifactor authentication - Microsoft Entra ID | Microsoft Learn
For a single global administrator account, the only way to recover it is to call the Microsoft Business Support global phone number and speak to the AI to direct you to the right support team.
Customer service phone numbers - Microsoft Support
Based on reports from users in the community, there are possibilities that the AI is not smart enough to understand your speech and will not direct you to the support person. You may need to speak slowly and clearly to the AI. And some users may need to try several times to call and contact the right support team at the end. In this situation, be patient and try more often to contact the support team.
To check how to make a successful call, see the following two success examples:
I can't log in to my administrator account - Microsoft Community
Microsoft Authenticator does not notify you of the CODE - Microsoft Community
Regarding support hours, Microsoft’s business support hotline is generally available from 9 AM to 5 PM, Monday through Friday (local time). However, availability and language support may vary depending on your country or region. For more details, Find Microsoft 365 for business support phone numbers by country or region - Microsoft 365 admin | Microsoft Learn
If an organization's Office 365 Business/Business/Education subscription is from a syndicated partner or reseller, and if the global admin can't open the service request on your end, you might need to contact the reseller's support provider so that they can help the global admin open the service request on your ultimate heir. after the Office 365 support team participates in the service request created.
Please note that anyone here, including community moderators, is not qualified or authorized to help regain their access to the global administrator account. The above method is the only official channel to help you on the matter.
I hope the above information is clear to you. Your patience and cooperation are greatly appreciated.
Sincerely
Feroz Mahmud | Microsoft Community Moderator