Confused accounting

I have settled a loan on 2-10 2018 with RCS through my Bank. The settled amount paid in was in excess of the amount owing. On the 8th of 10-2018 i called the call centre to confirm the payment had been received and was told that it was received and there was a credit due to me of Aprox R1200. On the 10-11-2018 i called to confirm when payment of the credit can be expected i get told i will be paid upon completion of the refund process, I was then told that the refund was R 400.00 less due to accrued interest. Ok.. As the accounts only closed after my payment was received, I AM STILL LIABLE FOR INTEREST OF R400.00 FOR TWO DAYS??? Logic defies me here. The account was settled on 2nd of October so its now in positive balance. SO YOU OWE ME INTEREST OF 27.5 Percent for monies in credit. How can i be charged interest for monies i do not owe and R 400.00 at that.. Blatantly this accounting does not make sense to me. My cell number is ********** 545 if anyone can explain the principle of i owe you interest for an account that is in a positive balance i would love to start a business that way as i would be retired in no time at all.... a win win for me both ways.