Couples Therapy Exposed review: I don't know how to stop charges

I signed up on the website of company Couples Therapy Exposed. I paid for the registration and it cost me about $20. I never used any other services of this company, but they started to charge me for this sum every month. I already sent them emails and asked to cancel the fraudulent charges, but no response. I wonder if there are people, who had the same thing. Maybe you can advise me how to stop these withdrawals. Please post your ideas and comments. Thanks.