Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
From your message, you have a primary Global Admin Account that you are locked out of.
You also have a backup Global Admin account that you have never used, and now you found that you are also locked out of.
You have limited recourse in this case.
I would assume you have no further Global Admins that can reset your account
Did you purchase your license from a reseller? Do they have delegated admin access?
If neither of this work, you will have to raise a support ticket.
You can do this by calling the support hotlines, or creating a trial account and using their support page to raise a ticket.
If you choose to call, they do have a Interactive Voice Responder that needs to be carefully navigated
People have found this script works. You may try and see
IVR: What kind of problem are you concerned about?
You: Authenticator.
IVR: What kind of product do you use?
You: Office 365 for business.
IVR confirmation: education or company account?
You: For companies or For education
IVR: Are you an administrator?
You: Yes.
IVR: Do you have the other administrator in your organization?
You: No.
IVR: Do you need a... Service request?
You: Yes