[ParisEngLtd]

They had no right to take your commission, if they change their T&Cs they can't do it retrospectively, you have spent out money advising their company on the terms they published and you are now out of pocket. If you have got nowhere with CJ I would write to someone high up in the company directly (and politely in the first instance) as it is probably a jobsworth who is responsible for clicking the button to reverse the commission.

I wouldn't mention 'exploiting a mistake' though, I would put more as a standard practice for promoting a merchant that doesn't ban these activities otherwise you are kind of implying you knew you were doing something wrong!!