EFT Reversal

A payment was made into my fnb account by an nedbank client and when she tried to reverse it she was told that she needs to contact fnb and when I tried to get fnb to assist they advised that Nedbank needs to contact fnb and then the payment can be reversed. So what I’d like to know is who exactly is supposed to assist and who will assist since none of these banks want to assist!??? Can someone please call me and assist as this is an urgent matter my business account is in a minus and I don’t have the money to replace the money transfered.