MTN contract cancellation hussle

I took a sim only, data contract for 24 months which I was paying R299. To my suprise after 24 months the contract was not cancelled nd now i was debit R540. I tried calling to cancel the contract without any success. Two consultants called me regarding the upgrade but still no success. I went to tge shop to cancel only to be refered to calling 135. Come month end I will have to pay R540 againg with this going back and forth, calling, going to the shop and online. This is incompetency. Why the hussle when 1 needs to cancel the contract. Wasnt it supposed to be canceled automatically after 24 months?