If you have an account there, the coins should still be available there, as technically they have not moved. If they're not showing, then you'll need to contact the support for the site you used and ask them for assistance.
Also, do you have some sort of transaction history available on the site? If so, maybe double check the transaction IDs for your coin purchases and make sure they're the same as what the wallet is showing. It's possible that the transaction information you see in the wallet might be incorrect due to it actually being from another network.