Overcharge on banking by FNB.

I have a Gold cheque account with FNB without an overdraft. I noticed that FNB charges me a fee every now and then after they have debited my banking/service fees. This charge 'Items paid no funds' is supposedly because they honor a transaction I made when I had no funds. When I investigated this on my account I found this is a blatant lie. I made a purchase when I had funds, obviously the merchant didn't bank it immediately and obviously the bank reserved the funds I had in my account for that transaction. Then my bank fees were debited and put my account in a negative balance, but FNB then used the funds reserved for the purchase I made previously to cover the bank fees and by the time the merchant banked the transaction there was supposed no funds. I feel that it is absurd for FNB to be charging this fee, knowing I had money when I purchased to cover my purchase, also knowing that a merchant never banks something the same day. Also knowing that I have no overdraft so if I essentially swipe my card and don't have enough money my transaction would decline right there at point of sale. It's very clear that FNB never takes it clients seriously, I have complained many times and my issues is never resolved, how do you charged someone R359 at this time of CORVID 19. Why that charge when they can see there was money at the time I bought and it is the process between banking the transaction and what happened in between when the bank debited my banking charges/fees that pushed my account in a negative balance. Why must I the client then pay the bank an extra fee on top of all their already expensive charges when the merchant banks after the bank debits my banking charges/fees monthly? The bank knows very well they did nothing for me. They did not honor any payment for me. This is day light *******. I get nothing for free so why does FNB expect me to just hand over my hard worked money to them? When I investigated my last I have picked up that FNB does this every month when I happen to make a purchase when I have funds before my monthly service fees are debited, then they put through their fees, it takes up the funds that were reserved for the purchase I made, the bank fees pushes my account into a negative balance, and the merchant banks the transaction the woops there comes the charge 'Items paid no funds'.This is ridiculous. And I am sure I go back further I would find it on the prior statement too. But then again I can't go back further to check otherwise they will charge me for a statement as well. The call centre consultant and her team leader was of no help. They were not thinking outside of what they were reading on their screens. They could see what I said to them about having had money to pay for my purchase at the time I bought but it is their bank fees that used that reserved funds every time before the merchant gets to bank. I mean they also know very well if I really didn't have funds when i purchased I would have been declined there and then at the till. The only thing the supervisor said is they have no control over when transactions are bank, duh obviously and the only thing she can do is make my service fees billing date same as my salary date and she can send my query to reverse those charges but it will decline because it is valid. How conflicting. And how ********* of FNB