I was penalized for a debit i have no control of

I would like to raise my concern about my bank Fnb, on the 29/02/2016 there was a debit that came out of my account that I don't know. I tried to stop the debit but it doesn't appear on my online banking list, when I go to Fnb branch to request a reversal of the debit I was told that I will be charged an amount of R50. My big issue is we agreed with Fnb that they will send me an SMS for any new debits asking if I know about it but that only happened couple times and it stopped. I don't feel my money is safe with Fnb anymore because every month I go to the branch reversing those debits that I don't know and get charged for that but Fnb is the one that could not keep what we agreed upon. I think its time I try other banks because its only Fnb that has problems with these **********