FNB payments don't go through.

I made a payment via FNB App to a recipient that I pay every month. I got proof of payment and I sent it to the recipient. 10 days later the recipient contacts me and claims that she has not received the payment. How is this possible? when I queried this with FNB they were unable to confirm that the money has arrived in the recipients bank account. All they can confirm is that the money did leave my account. How is this proof of payment? This is only proof of an attempt to pay. FNB systems are not robust enough to ensure the money is deposited in the applicable account of another bank. Therefore they are not trustworthy to carry out my payment instructions. Even if there is a problem at the receiving bank, there should be some sort of handshake where the receiving bank confirms the payment. If not then the payment should be immediately reversed and I should be informed. Refilwe the banker says I must give FNB 5 to 7 working days to investigate. It is already 10 days after the payment was made.