If the recovery form was already rejected, I’d try it again rather than looking for someone to manually override the account. Microsoft says the support team generally can’t manually change the security details or send a password reset for a personal Microsoft account.
When submitting it again, try to use a device and location you normally used with the account. For an old account, include as much older information as you can remember, including previous passwords, old contacts, email subject lines, Skype/Xbox details if applicable, etc. Microsoft says you can make another recovery attempt, up to two times per day.
Also, if the attacker removed all your security info and you see a message saying the security info change is still pending, there is a specific option to report that you didn’t make the change.
The Microsoft Sign-in Helper is also worth trying first, especially since the account email/security information was changed.