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.
The link below contains the transactions I cut and pasted from my profile, and the response I got from Bittrex. I never disabled 2FA, and the API key got changed at around the same time stamp, I am not sure if that is significant or not. (I still very new to crypto-currency as I have just started).
I am not sure what Bittrex can do for me at this point, as they haven't replied to my request for an investigation.
Removed link