Contract cancellation gone wrong

My 3g contract expired in August this year but somehow the call center agents don't want to fully cancel the contract. Everytime I call I am being told that my contract is canceled but I still get debited R18.00 every month. When I check I again I am told that this is for me to keep my Sim active. Please take your Sim and 3G and stop debiting my account. I am tired of calling your call centre monthly and not getting assistance. If you listen to the recordings I get told that there will be no more debit orders but yet I still get debited.