Hello. There might be a way for you to get your account back. And everyone in this conversation too.
Although the microsoft support part is fully automated and does not have anything against our cases of hackers changing our informations, the XBOX support, which is linked to microsoft, does feature a way to call or text a HUMAN operator.
If you remember the old details of your account, they may transmit the info to the engineering team, who might be able, if you can prove with enough info that you are the previous account owner, to reverse the changes.
If they cant reverse the changes there is a procedure to transfer the xbox game info, such as minecraft info, gamertag, ect, from an infected account, to a NEW account, if u can prove the infected account is (or was with old info) yours.
I am currently undergoing these procedures, they promised to give an update in the next 7 business days.