Bank moving funds before installment goes off and then charges me insufficient funds penalty fee

So, I`m contemplating moving banks because FNB was unable to offer me feasible credit offerings after my divorce, which I since successfully sorted out with another bank. So, i closed my credit cards, overdraft and downgraded my cheque account from Premier as i`m still unsure as to moving banks and debit orders are worth all the effort. So in the meanwhile i just leave in the required amount for all my debit orders to go off successfully, then as a cheek the bank decides to move funds before my last debit order goes off and then charges me an insufficient funds penalty fee. I then phone the bank to tell them about it and the agent Pamela, (manager`s name is Veron or Sarhaan) goes into my account and then can`t find a reason on the system as to why the penalty fee was app**** because as soon as I saw my account needed more money i transferred it from another account. Then she transfers me a non existent number and drops the call. FNB is of late become really pathetic when it comes to service and the s**** of the staff in wanting. IF ANYONE IS CONTEMPLATING MOVING TO FNB, DON`T!! RATHER GO TO STANDARD BANK OR NEDBANK... EVEN THOSE 2 BANKS HAVE BETTER SERVICE.