contract cancellation

I have been trying to cancel my contract since last year as it had already ended but there were still deductions ( I don't know exactly for what ).They requested me to contact Retentions department as they cannot do it in store, I called 4 times and held the line for almost an hour every time and eventually my call got dropped all the time and I sent emails (which I am still awaiting response)from last year September. Eventually informed customer care that im going to dispute these debit order at my bank because im paying for a contract that ended last year June, i no longer even have the phone nor the sim card but they change the debit order and they now deducted 3 times the amount that i was paying. I dont understand why they making it soo difficult and how am i paying for a service that im no longer receiving from last year!!! im not even using the network anymore mxm. Im done with these contacts its funny how you can take out a contact in store but you can not cancel it in store. Does this Retentions department even exist???