Bad service ever

Last month I went to one of fnb branches because I had deductions with ref #ITEM PAID NO FUNDS,everything was explained to me that it is when I don't have funds on my account then fnb will pay the debit order then they will deduct from me as soon I have funds on my account. I request that option to be canceled and I was told they canceled,to my surprise I woke up with a deduction of R200 Ref# ITEM PAID NO FUNDS I thought that option was canceled. I want fnb to explain to me because honestly I don't understand.