Like everyone on this thread, I received a series of notifications that all my security info and 2FA had been removed within 60 seconds.
Like everyone else, I got the 'account doesn't exist' message when trying to recover the acount.
I contacted MS chat support, and they acknowledged the issue and had me fill out some form to upload for higher tier support.
Then they asked me to wait 24-72? hours for a response.
In the meantime, I found the full ru address in the notifications I received.
I was able to use the ru address to attempt a recovery, and somehow that succeeded, and changed the password.
I am now the unhappy (co?)owner of a ru email address microsoft account.
Changing the security info requires waiting 30 days, so I'm stuck using the ru address for now (apparently it's still associated with my xbox gamertag).
I still see the original email address in the Other Email Addresses, but it's not really usable.
Will the culprit try to reset the password during this 30 day wait? Hope not.