Bittrex is not responsible here because Bitrex always sends notification emails if someone logs in using a new IP address. You can track the address where your BTTC is gone but you cannot do anything to get it back. So you are your own security in the crypto room. make sure you are aware of this in the future by being careful with your private key and don't let anyone have access to your computer. hope bittrex will help you get your coins back.