The Short Answer: WINNERonline's Gambling Message Board
It's unfortunate but players sometimes have trouble getting paid. There can be two reasons for this. The first is that they can't pay you for whatever internal reason. In this case it's unlikely that you'll get your money. The second case is that they'd rather not pay you if they don't have to. In this case it's in your best interests to convince them that they really should.
It's my belief that in both of the above cases the only real hope of satisfaction is to go public with your case. And the best place to do that is the message boards. Our is the biggest, most read in the industry so if visibility is what you're looking for, http://mb.winneronline.com is the place to get it.
Go there, read some of the other posts to get an idea how others have gone about it and post something of your own. Don't be antagonistic or hostile but do state clearly what the issue is, how you've tried to get get in touch with them, etc. Name names, be specific. The chances are pretty good that someone out there will know something about your problem and be able to help. If nothing else you'll be warning other players about a site that isn't honoring it's obligations.