Settlement amount

I had a loan with Capfin and the last installment was due the 30/06/2015, I had skipped one premium in January and agreed to pay this on the 31/07/2015, which was a total of R1414.04 including interest. I even received an sms confirming this amount would be debited from my bank account. On the 30/07/2015 Capfin debited R1039.72, I sent an email asking why this amount and not the R1414.04 as advised telephonically, seemingly none of your consultants know why. Then on the 31/07/2015 R374.32 was debited. Again I sent an email and was advised that the amount debited was the installment excluding interest and now I owe R57 to Capfin. Why do I still owe interest but the amount quoted on my settlement was R1414.04??