FNB

So I know how the FNB cheque account works e.g. the available and balance part , but when there is funds for a certain debit to go off and days later when you sure it did but then you get a sms saying you didn't can make you a little angry. Then what's worst you end up with more funds in your account that the lord alone knows where it came from , I must say I'm so ticked off with fnb and their stupid system I'm really thinking of changing banks.