Then this should be someone close to you, maybe try reach out to your friends who often share same system with you or could be a friend you hand your phone over to. How is that possible for a hacker to have full control over your btt account as same time with your mail.
Not really someone close. Supposing the email attached to the account isn't some throw-away email that is used only on the account, there are chances of other usages that could have lead to giving the mail off. Like from your TRC20 address presented in OP, it means OP has been about some bounties at some point and could lead to some email exposure in filling out some forms and subsequently, compromise.
It's good enough the mail address wasn't swapped and even better now, the account has been locked due to recovery via secret question so, you stand a better cjnace at unlocking by following the processes as given above by _Blackstar in proving yourself and when that is done successfully, you do your hit to ensure privacy and security by changing important access points @OP.