Honorary Fee

I checked my bank statement yesterday and noticed that on 12/06/2015 I was charged a honorary fee for two transaction which was done on 28/03/2015. The R180 was debited to my account almost three months after the two transactions. I find it unaccecptable. First of all why was my card not declined at the till on 28/03/2015 if there were not enough funds and why after these two transaction could I still go and draw R600 from the ATM later that afternoon? I phoned nedbank this morning and I was told they had a systems error during March and April. My question still remains why must I now after almost three months pay R180 for a systems error. If the system was up and running I would have been declined at the ATM to withdraw the R600 but my balance available at the time of the withdrawal showed that I could still draw the money because the system did not show the two transactions I made earlier the morning was pending? I want this R180 to please be reversed as it was not my fault as I cannot authorise any transactions, Nedbank is the only entity that could do that..