cancellation and refund from Cell c

I took a contract with Cell C, which was supposed to end last year(2017) December. To my surprise they are still debiting from my account even now. Why? The way they call and request for payments when you've missed one payment should be the same way they should when they make mistakes like debiting on my account for 7 months even though I have completed their payment. I need my R195 paid back starting from January, because I haven't been using their services.