Bank charges

For the first time, im moving all my debit orders from FNB, like how does one be on -R680, ive been transacting and there was pending fees that were allocated for and when they had to clear, im suddenly on -R680, the available balance was in short of R109 from to cover the last debit order on the 25th but we are here.

They making money with charges but this has to be ridiculous thing ever!