I just got scammed by Reading America. Has anyone ever managed to cancel? How?

I stupidly agreed to pay $40 a month for 7 magazines and was told that i won a $1000 shopping spree. I then proceeded to look online at the company and discovered this is a big scam and most people never recieve their magazines. They won't let me cancel. I'm going to attempt to cut them off at the source, my credit care. I'm just worried that I will be doing something wrong for not paying.