Moving banks

I am a privat client at Fnb. I made an electronic payment into the incorrect bank acxount by mistake. I immediately contacted the bank who sent me a reversal form, I filled it out and returned it. Seeing that the transaction is not finalised, I assume that Fnb can return the money (at a fee) to my bank account. I used the secure chat function to find out progress today. I was told that it will take 10 days to possibly return the money. There is no gaurentee. Clearly-the money was not paid to the incorrect recipient account yet. Why is this a matter of "possibly"?