Happened to me this morning as well. The web address prize-help.com resolves to http://findsupportonline.com/incredonline/.
Findsupportonline did deal with a legitimate registration to an adult site for me, but they didn't send any confirmation and appear to just start charging the card furiously for all kinds of stuff. I definitely unticked any extra tickboxes when i registered. Cancel the card at your bank before dealing with them, because if they know the details they may try to squeeze another charge through. The charge to prize-help.com appeared shortly after they had confirmed my cancellation for the actual site I had registered to.
Or if you've never dealt with them or just don't feel like it, don't contact them at all. Just cancel the card and start fraud proceedings with your bank. findsupportonline has a warning about doing this on their homepage so I'd say its the way to go. I've seen some reports of charges from prize-help.com that came completely out of the blue so this may well apply to you.
I'll never put my details on any page that hasn't redirected me to ccbill server or similar trustworthy credit card processor again. For the record it was an incredible pass and i should have known it was dodgy from a mile away.