Debited incorrectly and funds take a week to get paid back

I had a Personal Loan with FNB which I settled on the 20th of April, but despite this a debit order created by FNB went off for the Loan on the 25th of April.

When i phoned on the 25th (Thursday) I was told I need to wait until the next day for the payment to reflect, before it can be paid back. So on the 26th (Friday) I phoned again and someone processed a refund/reversal of the funds, and I was told it will take 3-5 business days for the funds to be back in my account.

Today after 3 days, I still have not received the payment, and tomorrow is a public holiday, so I am guessing I will only have my money back on Friday the 3rd of May, one week after the money was incorrectly taken.

Why does it take 1 day for the money to go from my FNB account to the bank's FNB account, but I need to wait 5 working days to get my money back? That is ridiculous. Please can this be sorted out and my money paid back to me.