FNB Charged me R150 for a R26 Transaction

Good Day, I am very disappointed with FNB. First of all I have been charged R500 honouring fees as they say I did not have enough funds. I was not aware that my account had insufficient funds. I would have expected my card to decline if I have insufficient funds. I have never had a negative account since I banked with FNB. How does FNB explain charging me R150 for honouring a R26 transaction?? I have been also changed R350 for 3 items, I don't know what that means. I have tried to call numerous times but 3 times, I went to an extension where the person is not available. I refuse to pay such a ridiculous amount, the banks should have declined my transactions. I am trying to call but I a being put on hold and the people I speak to are not sure as to how to answer my questions. Can this be rectified otherwise I will have no choice but to move to another bank.