Fnb does *****ulent with Excess Item fee 1 Ite Ms.

I have a problem with #Excess Item fee 1 Ite Ms... I did transactions on my account when I had money ..and when my account went on zero,merchants came to collect their money and Fnb charged almost a R1000 + for the collection in the name of Excess fee.. I called the bank and they can't even defend their case,they keep on saying to me that I did transactions even when my account was on a minus which is not true it's the collection of merchants...they really do *****ulent on clients