Managing personal Outlook.com account settings, security, and privacy
I understand your frustration; however, once a hacker is able to modify the account's security information, there is nothing that can be done to recover the account.
You may try reaching out to Microsoft Support immediately, as they can possibly "Suspend" the account permanently once they have confirmed that the account can no longer be recovered in order to prevent the hacker from using it:
Type "Microsoft 365 sign-in problem" > Click "Get Help" > Scroll down and select the option "Sign in to contact Support" > Microsoft 365 and Office > Billing and Account Profile Questions > Confirm > then select "Chat with a support agent in your web browser"
Best regards,
Darhyl