May be you can provide any proofs. Some screenshoots, transactions or anything else? Quite big exchange may be some mistake? What do you mean dont credit account?
Nothing perfect in the world unless god (if you believe).
So even they try to do the best and they will have mistake. So you need to check to them first to make sure. The support will help you i am sure. Actually i never face this kind problem so i am ok with the exchange.