We need clarification on ITEM EXCESS FEE

I still cant make sense of ITEM EXCESS FEE i mean i love my bank but I cannot deal with this: How do you explain to me I have funds in my business cheque account and i swipe for item A, B, C, D. I run out of funds. Overnight i get a charge on my card that throws my account on minus. Then the following day im receiving R155 charge as ITEM EXCESS fee against item A, then another one for item B? These items were paid for while there was funds in my account why am i being penalized for transactions that were honored??? Now every morning i wake there is an new ITEM EXCESS FEE come on people!!! I googled this and there is no clear explanation out there!