Cell c horror cellphone contract

In 2016 I joined into a cell c cellphone contract and paid the phone up until 2018 two years exactly, I noticed they were still debiting from me every single month . I went to cell c the store at the mall at Mall of the South the guy told me my cell is post paid I then reversed the debit order . Now 2 years later they are still calling telling me to pay reversed amounts , I was paying the phone for more than 2years and some month . They supposed to let me as their customer know that the contract is ending instead they keep debiting and tell me I’m supposed to tell them when the contract is ending . Who’s the business supplier here ? I’m disgusted with cell c!