FNB removes money from my cheque account and then charges R90 to honour a payment

FNB I am fuming now. I have a cheque account and a savings account. I keep my money in my savings account and just transfer enough to the cheque account now and then if I want to make purchases. Sometimes there is not enough money in the cheque account and my card is declined. Fine. Then I just quickly transfer more or pay in cash. BUT. Now FNB decided ON MY BEHALF to pay for me and CHARGE ME R90!!!. For the FAVOUR or whatever you want to call it. NO!!!! PLEASE NO!!!! DECLINE MY CARD AND I WILL MAKE A PLAN. Do NOT pay on my behalf and then charge me for it!!!. ESPECIALLY if you took MY CHANGE OUT OF MY CHEQUE ACCOUNT AS YOU SEE FIT and dumped it in my savings account so that I have less money in my cheque account THAN THE LAST TIME I CHECKED. And then try to buy something because I am under the impression that there is a certain ammount in my account. But no! FNB took MY CHANGE so that my account. Please let me know how can opt out of these options. NO Bank my Change and NO PAYMENT ON MY BEHALF. Please.