Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
For Microsoft 365 on Mac, the supported way to reach a person is through Microsoft Support.
Use Contact Microsoft Support: https://go.microsoft.com/fwlink/?linkid=2258335
If activation is the issue, Microsoft also directs Mac users with activation problems to contact support here: https://support.microsoft.com/en-us/contactus/
If the problem is specifically with signing in to the Microsoft account, start with the Sign-in Helper: https://go.microsoft.com/fwlink/?linkid=2214157