Nedbank settlement amount for personal loan a ripoff with interest for 7 coming days when loan settled today

I request a settlement letter for my personal loan today, and the difference between outstanding balance and settlement balance is R2600. my debit order for the loan just went off yesterday. They say the R2600 is interest for the next coming 7 days. How can I be charged interest for next coming 7 days when I am paying off the loan today, meaning I am being charged interest of R2600 for the next coming 7 days on a Rnil outstanding balance. This is wrong and a rip-off. The person I spoke to at Nedbank says it's how the system operates, the amount is calculated by the system. but the system is wrong, you cannot be making me pay interest on a Rnil balance.