Since that guy is also using coinbase and the only way for you to re-claim your bitcoincash to create a ticket support to the coinbase. if the address that already used by that guy is coming from the personal wallet that he can get the privatekey and it can be claimed easily. But since it was controlled by coinbase and the coinbase itself can fix this problem to access your BCH.
Just create more and more ticket.
The recipient, who is the receiver, definitely cannot own the private key and if he does, under normal circumstance, most especially for personal wallets, it cannot be retrieved, but since they are both on the same ecosystem, which is Coinbase, the support of Coinbase should be able to fix it. .Just create more and more ticket.
Although, in some cases, some exchanges might charge some fees to fix that.
The OP should just contact them and wait for response from them.
If they do not respond on time, do not give up, you just keep contacting them, but pls, do not use any other means that is not recommended by Coinbase, aside creating a support ticket, because you might get scammed if care is not taken.
Once again, do not give up.
