FNB dropping ball

I was paid R15 000 from a Standard Bank Business Account via EFT on the 7th of December, 2023. The payer made an immediate payment and sent proof of payment. The problem was that the Zero Account that they made payment to had a monthly limit, and the payment bounced - so the money never reflected on my side naturally. When I called FNB to find out what the process would be after this, I was told that the payer should expect a refund to their account 3-5 days later. Almost a month later, the payer hasn't received their money, and Standard Bank has sent various written proofs with tracing codes that the money left the payer's account immediately and was honoured on the FNB side. They advised that FNB should look for the money in a suspense account. FNB, on the other hand, is adamant and insists that the bounced amount is sitting in the Standard Bank suspense account! What I find odd is the insistence by FNB that they do not even see or monitor money that bounces back! Interesting! I made 5 visits to various FNB branches, and I was sent from department to department (on inhouse phone calls). I also called the call centre on various occasions, and no help came forth. My question is;-how can a bank have incoming money that is not recorded as inflow, and how can money bounce back without the system noting down the error and the reason why it bounced back?! More than 3 call centre agents swore that the money was not recorded and is sitting somewhere in the Standard Bank system! Where is the money?