Is the Bank making unfair money out of clients?

I was told to go into the Secunda branch to cancel a debit order from the NPDA NPDA***, as it cannot be done telephonically. I did the paper work at the branch in 2014 August. Since this time the bank let the debit order go through and charged me R155-00 as there are no funds available, although I physically went to the bank to cancel it. How is this possible that they let it go through continuously after the cancellation and making money out of me?