Theft at it’s best

I sometimes worry about FNB, this charge “Item paid no funds” is the biggest **** ever, you have a certain balance on your account, then you pay or swipe, knowing full well that your payment is valid, next thing you see FNB charging you R135, for not having enough funds for that transaction…I mean if I have R1000 in my account and I pay R300 and I’m then left with R700 how is it possible for them to say I didnt have enough funds then charge R135 for that, please reverse that R135