Account debited

I have an access facilities with capitec and pay via debit order. On the 25th November capitec debited my account but never allocated the funds debited to my access Acc and I kept on receiving msg that my account is on arrears. I called them and the told me that from their side it shows that the money was collected but the is a system error. Today the 1st December they have charged interest on my account as in the account was not paid. I called them again and bn told system error. When I tried to explain that if system error why are they charging me interest as in the account was not paid no answer and I was put through management complain line were I holded for 30 min with no answer.

Why if is their system error y am I bn charged interest for unpaid account? And this is messing with my credit scoring. And is like to them is a game