That's not how vac works, you can only get vac ban while playing on a vac secured server.
If I understood correctly someone wrote you'll get a vac if you don't deposit your skins on another account?
^ This itself is an obvious scam attempt, but since they already got into your account, best thing you can do is:
- go to steam > settings > account > manage steam guard security
and click "deauthorize all other devices" which means if someone is logged onto your account on a different machine, it will log them out.
Then simply change your password and problem is solved.
btw, do you not have mobile authenticator??