Sorry, but resolving the problem is almost solely between you and the other party and your bank/paypal. Coscom usually refuses to get involved beyond anything more than banning a user from posting more ads, and that's only in extreme cases, not when it happens to just one or two people. As per this post below, and I quote,
It is up to you to research who you are working with, especially when it comes to commissions. We do NOT get involved with any personal disputes. Recently we have had the pleasure of the same 5-10 users nailing our PM inboxes with so much he said/she said crap to the point of it becoming absolutely ridiculous. Unless you are complaining about a direct violation of our overall site rules, your PM will be IGNORED.
The most that can be done with this site is checking out the comissioner review forum, there's a lot of users on there that have dealt with resolving problems/scams/etc. and may be able to help you figure out what to do.