FNB not able to located money paid into an FNB account while there is a proof of payment

I transferred money from Nedbank to an FNB account on the 8th April 2020. Nedbank issued me with proof of payment and they conferred that the money was successfully transferred to FNB. However, the money is not reflecting on the FNB account and FNB is sending me from pillar to post. I have called their national call centre and visited a local branch several times with no luck. The staff members that I spoke too told me that there is nothing they can do. Surely money cannot disappear into thin air while I have proof of payment.