DSTV Credit?? What the heck!

I got a call today from Debt Collectors telling me that I owe DSTV a sum of money on my account. I never signed up for credit with DSTV, and as far as I know they're not a credit privder, so how and why did they give me credit which I did not consent to on a prepaid account? I'm told that DSTV didn't know that you no longer want to use the service - well, I still have their ugly decoder with me that I paid a lot of money for, so what am I going to do with that? And how exactly did they know I'm not going to use the account ever again??? So now we unwittingly get signed up for contracts without our knowledge? DSTV never clearly specified for me that I'm incurring debt by getting their services, and as far as I know I signed up for a prepaid service. Is DSTV a credit service provider??? What the heck is going on with this horrible company that feeds into the pockets of the filthy rich by robbing the very little cent from the man on the street? Really?