Exchanges have their own terms and conditions which you agreed to while creating your account, probably you didn't even read anything in TOS, just clicked agree and created it that's why it comes to your knowledge only after it happens.
The reputation of the exchange is not great either and the coin you're talking about is traded on any other exchange or just on HitBTC?
You're wrong, sir!
I read them carefully and I know exactly what I accepted.
There were no such taxes, but they were introduced later "illegally".
Not informing about changes is illegal. In 11.3 they guarantee to do so and by the way they violate the law in countries where they offer their service. That's how a thieve justifies his theft.
As said above you might missed them to read because these kind of information will be buried under documents that we don't give attention to and even if you're strong that you have been cheated by the platform it's not going to be easy to take legal actions against such entity. So if the amount charged is manageable then accept and move on, withdraw any balance left in their and pick the right platform in future and always remember exchanges are not meant for long term holding.