Failure to deliver support to a loyal customer

I am a private account and bussiness account holder with FNB. I had an incident last week where I withdrew money from a Nedbank ATM because 2 FNB ATMs were not working in that area.The ATM didnot dispact any money, however money was deducted from my FNB account. I am now being told to go to Nedbank.I am not a Nedbank account holder and cannot be dealing with Nedbank whereas FNB authorised for the money to be paid to Nedbank. FNB continues to offer terrible customer service. I am currently looking for a new bank to deal with.