Deducting money for a contract that does not exist

Cell C keeps deducting money from my account even after I cancelled the data plan.

I had a small mobile data contract that that expired and turned into a month-to-month data plan years ago, about 7 months ago I tried to stop the month to month payments on it. Went into the shop and did everything they asked.

They kept deducting money from my account each month! Eventually I got fed up and stopped the payments with the bank. This helped for a while, but now they started deducting the monthly payments again!!!!