Ilegally debiting funds after Cancellation

After a struggle to cancel my contract, I finally managed to cancel my phone after my contract was ready to be cancelled. My contract was cancelled from April 2015. No funds were taken from my account. This month you decided to debit my account for no reason. I went back to the bank to reverse this. Only for you to go and debit again??? Please kindly inform me, what is this that you are debiting me for as I now have a prepaid account with the same number that was on contract? Can you please wake up and stop *****ing money that you have no claim on!!!!!