You should have moved the BCH to another wallet before the fork.
Below is the tweet they made before the Bitcoin Cash fork.
So it's a case of "not your keys, not your coins", as always. By my definition anything that doesn't give you access to your own keys can't even be called a "wallet". It's more like an exchange.
If their policy isn't considered theft or negligence I would be amazed.
Many exchanges did this with many Forkcoins. Most Forks aren't worth the money, but this one must have been a nice instant profit for them.