Nedbank authenticating ******* debit orders

My FNB acc was debited as follows FNB :-) Paid from a/c..16 Mar: Ref. Billion Rf***7bill8333. FNB gave me the culprit's number. Its Nedbank. When I contacted Nedbank they wouldn't divulge the details of their 'client' but referred me back to FNB and said they should contact their back office. FNB knows nothing about that, they said to me they had already given me everything they could on their side (Ref & contact #) when I went back to Nedbank, still cannot give info for their clients I should go to FNB which intern should contact their back office with this query whilst FNB would not do this. Why is Nedbank protecting these *********? I demand that Nedbank provide me with valid proof that they acted in accordance with the instructions, given to them, by me or your client on my behalf, by means of telephone or facsimile transmission or by email at a time when you set up your system to have my personal account debited by your company. Please note that I have a valid right to challenge the validity of your debit order initiated against my personal account and that you as a debit order collection agency did make the necessary verification of the records sent to you by your client