My account has been hacked

My primary Gmail address associated with my Microsoft/OneDrive account was hacked. The attacker accessed my Microsoft account, changed my password, and added their own email address as the primary alias/recovery method.

Here is the current situation:

Password Reset: When I attempt a password reset, the verification code is sent directly to the hacker's email address.

Account Recovery Form: I filled out the Microsoft Account Recovery form, but it gets rejected automatically within seconds. The form lists the hacker's email address as the main account holder and states my details do not match.

Current Access: I am still logged into the account on my PC, but I cannot authenticate into OneDrive or modify security settings because any prompt defaults to the hacker's email.

How can I remove the attacker's email address and regain control of my Microsoft account when the primary alias has been replaced?