Contact cancelled but still taking money

I had an mtn contract which I called to cancelled in Sept. The guy I spoke to said no problem it will be cancelled. I then called again begining October to confirm if it was done they then said I can only cancel on the 19th of October. I called on the 19th October to cancel the guy I spoke to said he will send the request through. I explained to him that I am not going to pay for another debit order. He said that if I do receive airtime I should not use it then they will reverse it. When I checked my airtime balance all my airtime was gone and they still debited my account again. I want answers why are they still deducting from my account and took my airtime. My reference for the call was ***......