Prompt payment results in interest and threats

On 30th September, my mother paid both my and her Foschini accounts via EFT. On the 5th of October, my mother received an email that stated the amount she has already paid is still outstanding and that late payments will negatively affect her credit score. She then rep**** and sent her bank statements, which clearly indicates that payment was made on the 30th of September for both our accounts. We have both received our Foschini statements for the month of October now. Foschini has charged both accounts with interest of R168.75 for late payment. This is ridiculous and absolutely unacceptable. Foschini's accounts department needs to wake up. I expect a prompt response from Foschini regarding this matter as the interest will NOT be paid.