I don't know much about that wallet.  If you can get your BCH private key from the wallet, then you can import that private key into a bitcoin wallet to regain access to the bitcoins.  If the website does not provide you a way to get the BCH private key, then you'll need to contact their support.  They should then have access to the BCH private key, and (if they are willing to help you) they should be able to access the BTC and send them back to you.