I want cancel every policy that I have with FNB and close this account if you don't fix this

I had a a few debit orders in my account that were unsuccessful and now the bank charged me more that R105 per debit order, those payment didn't go through but not my account is on minus R5000 as if i have an overdraft but I dont and those debit orders failed and FNB is refusing to have a look and correct the R5000 bank charges.