Capitec has bad customer service

I had a loan, decided to settle it in 2014, went to Capitec to get a settlement letter. I paid it off a few days later. <br> <br> A whole year and more later capitec debits my account out of nowhere. I call and I am told there was an amount of 800 outstanding when I paid it off, that no one told me about and now it has earned interest amounting to 3400.<br> <br> my question is, I had been paying off the loan via debit order, the r800 could have been taken off my account the next month. why did they have to wait until it was 3400 to debit me out of nowhere?