7 Answers

I would visit the bank personally and talk to the bank manager.  If (s)he is unable or unwilling to provide a straight answer, I would encourage him to contact someone higher up who WILL be able to stop stalling.  I'd insist on something IN WRITING, too.
For certain, I would be on their butts with a phone call to the manager every day.

....were they technically hacked or robbed at an atm , or an inside job ?

....operations may be focused on protection/correction instead of communicating with their client.

....a call from your attorney may motivate them , if you feel they have had a reasonable amount of time to investigate/respond.

Go over their heads and talk to somebody who specializes in customer service. ... .

Change banks..>>>>>>>><<<<<<<..

PHONE UP THE LOCAL OR MAIN LINE NEWSPAPER ,AND GIVE THIER NAME UP FRONT TO BE SEEN BY ALL AS A BANK THAT IS NOT SAFE TO DEAL WITH,,LET THEM KNOW FIRST,TO GIVE THEM A CHANCE TO READEEM THEMSLEVES,,

So I called the bank this morning and was told that someone would call back. They did not.

I think this bank is taking the piss because they don't want my account and hope I  will close it and go elsewhere. The bank is Nedbank Private Wealth so that may give a clue as to their preferred clients being of high net worth which I am not.

I will call again tomorrow and keep you updated.

Someone from the bank called and apologised profusely and the missing money has been credited to my account.

This bank operates largely on-line and has very few physical branches, so a personal visit is not practical. This is the first problem I have had with them in 30 years, so I will keep my account with them unless there are more problems.