Debit order send back as unpaid

On the 1/8/2015 a debit order of mine was going of, there was not enough funds at that stage. 2/8/2015 Money was paid into my account. The debit order was subtracted and marked as paid! This morning 3/8/2015 I've received a notification that the debit order of R497 is unpaid and a R100 fee was charged for the debit order that was send back. I've phoned General Enquiries and after 15minutes holding I've spoken to Tebogo and he said the debit order was send back because my credit rating has dropped!! This is totally absurd!! I have to pay R100 for that transaction, as well as this is reflecting negatively on my credit record!! I think this is inappropriate for FNB to to this (for the first time in 12 years)!! This has never happened to me before!! I am seriously very annoyed with FNB!!