I have been debited 10 pounds a month from Shopperdiscounts.C, how do i stop this and get my money refunded?

I cannot remember how I came in touch with this company. I never benefitted from any of their services. I think this misfortune began with the order I have placed for some business cards long ago with vistaprint.com online somewhere in June 2008. It was one-off purchase and all transactions were settled. But when I checked my Barclays bank account today I was surprised to note that the SHOPPERDISCOUNTS.C REF 359 2227164800 BCC has been deducting a sum of £ 8.00 per month since then without consulting me. Please take action to persuade them to refund all the money they have deducted so far and cancel my account with them.