Trafficswarm or Scam?

My latest site that I have tried is trafficswarm. It's a traffic exchange program and it is free to join. They do have upgrade options, but I don't pay online for anything. So this is all based on their FREE membership. All you do is click on ads and earn credits for this. Then your credits are used to promote your urls and websites. At first this site was good and I earned about $20 just in a few days. However, this has stopped. I have sent two emails already asking what was the deal and as of today - no response. My credits are going down because they are being used to promote my url, but absolutely no hits on any of my sites. I've checked on my links and everything is working properly. I'm not going to say this is a bad site, but it's not great either. It also seems to me like they may actually promote your url properly in the beginning to "encourage" you to want to pay for the upgrade. The upgrade costs $30 per month, which to me is kind of steep. I wouldn't pay that much. But, to each their own.