If you received a notification that the security information was changed on your account and it is now indicated that your account does not exist, then that does indicate your account has been hacked.
I wish I had better news, this forum is just a user to user account and no-one here has any account access, when a Microsoft account is hacked, if the hackers change the associated data like the Email, then that account is usually no longer recoverable, try using the process they provide on this link to recover a hacked account, if this process is not successful, sadly, that account cannot be recovered.