What did Bittrex say? Its impossible to bypass 2FA and users of any exchange are safer if they have it enabled. So dont ever disable it.
tachypknea, contact Bittrex and post screenshots of the conversations. Also post screenshots of your Bittrex account transactions as proof. You can paint on the amounts for privacy.
You are raising a serious concern about Bittrex's security. We as a community should start getting to the bottom of this. Its either you are lying or Bittrex is not secure.
This is the best way to handle this is to contact the Bittrex support immediately. If thyis happens to you, it is possible to happen to anyone of us. Be sure to always keep your account/ password safe. For me, I did not activate my 2FA. I hope this is properly addressed and any breach discovered will be patch soon.