I also have had a run-in with said scammers. Kudos to those that have received refunds, I have been waiting for 2 weeks after being told that I would receive a refund. A note for those that actually manage to make contact with the company, here are some pointers I used (besides calling your CC Company). Keep in mind that I was a member for 3 months before asking for a refund!

1. Be direct and to the point like Edge said, don't be rude(I know, hard)
2. Check the website where you registered and read the fine print looking for "Satisfaction Guaranteed", "100% Satisfaction", or something to that effect and either print or save the page to your desktop.
3. Save any and ALL email you receive from them (I'll tell you why in a minute).

In my situation, after I found I was scammed (mp3downloadhq) I blew it off for 2 1/2 months until I told myself that they weren't going to win. I managed to get ahold of a representative via a phone number posted on one of these threads. I asked for a refund and the guy laughed at me saying that it was 2 months too late, until I told him that I had asked for a refund a couple days after signing up (not really true but got his attention). I mentioned that I had the emails I received from support sitting right in front of me (also not really true). After a couple minutes of being on hold, most likely from the rep having to ask his supervisor (the guy eating Cheetoh's next to him on the couch) how they wanted to handle the situation, I told him I would be more than happy to send screenshots of the email (refer to Step 3 above). Again, I was put on hold. Upon his return I was informed that I would receive a FULL refund. I said thank you, have a nice day and hung up.

Now, had he required me to send the non-existant screenshots I had to use an HTML editor, and even Word to an extent to alter the text/date/email address/etc. to conform to what may look like an official response from them. Then I took a screenshot of this edited email. Not really an honest way, but it was how I dealt with them.

The lesson that I learned is that making "threats" in this matter, as apposed to "I'm gonna tear your head off and..." are much more effective. In this case, they probably knew that they don't track what they send or receive, hoping that the customer doesn't either. Simply informing them that I had such documents probably worried them and rather than prolonging the process they just refunded it. Just some random thoughts from me...