Cancelled contract and 5 month down the line there is a debit order

I had a Cell contract that came to a end in Jan 2020 and I cancelled it. Suddenly in July there is a Cell C debit order from my account. I did not make funds availble in that particular account so the bedit order jumped back and FNB charged me R110. I call the call centre and was told to send a email to ***. However I did not get any feedback and yet again there was another debit order and agian I was charged R110. I called Cell C again today and I was told that they will forward my details to their legal department. I really hope to get this resolved. It is just costing me money every time and it seems that the big corporate companies does not care what they do.