Well, bittrex sends notification email wen someone logs in using a new ip address, unless your device was compromised, you should have that email.

As for reimbursement part, Bittrex is not liable here. You are responsible for the safety of your account. You can track the address to which your btc went but you can't do anything to get it back. Take it as a lesson, always use 2FA and never leave your coins on exchange unless you day trade. Move on. Good Luck.