How to return BCH with address BTC
hopefully this answer helps you.

Specifically,


  There is nothing which distinguishes a BCC address from a BTC address; they are both the same format and refer the the same keys, thus a BCC address is a BTC address and vice versa. This means that if someone sends BTC to an address that you created with a BCC wallet, the person who owns that BCC wallet would receive BTC. It won't appear in his BCC wallet, but if he has the same private keys on a BTC wallet, he would receive the coins there and be able to spend it.


Emphasis mine. Hopefully you have the private key!