Trying to force me to upgrade my decoder, & Auto renewal on contract

On numerous occasions, I have been called from a 3rd party company trying to get me to renew/resign a contract "as my decoder is old". I continually tell them I am not interested in renewing. Today I had another call about the same issue, and when I advised I am not interested in renewing, I am planning to cancel, I was told fine they will cancel!!!!!! and she put the phone down on me... Talk about being rude!!! When looking at my statement recently - as the debit amount seems to change randomly, I discovered I am on a "special 24 month deal" I then called to ask WHO AUTHORISED this 24 month contract - and as expected they could not tell me. So DSTV have somehow JUST RENEWED my contract some time ago WITHOUT MY CONSENT. Yes, my fault for not checking my statement monthly but that is NOT the main point. I cannot get hold of ANYONE who can tell who authorized the renewal, as I certainly DID NOT. Now I have 7 months to go, and I want to see if my contract is renewed automatically again, as then I will take legal action. I assume as they are losing customers and money, this is their way of trying to retain customers.