There are just some things that are not clear. Why did you send the money AFTER the fork, whereas the Bittrex statement said that only those who deposited a day before the fork would be granted the additional coins from the chain split? I mean, people don't receive the new coins if they do not possess the original one BEFORE the fork, right?
How is it not clear? He did the right thing by keeping his private keys to himself in the runup to the fork, and later send BCH to the exchange to either trade it or cash it out.
OP's mistake here is that he underestimated the consequences of an exchange not caring about the lack of replay protection, either intentionally or unintentionally.
It's once again a sign that people shouldn't be using an exchange as Bittrex. They hide themselves behind TOS they set up in advance, and there is seemingly nothing that can be done about it unfortunately. Stick to exchanges as Kraken and Binance, which seem to be the best hybrid exchanges in the game at this point.