Charged more than what's Due

This is my Last installment and my Monthly installment was 1475.44 and account was only left with R1394. 84 but I am still Debited my monthly installment with is more than what I am owing. How do am I being charged more than what is due I have a feeling I will still be charged next month with a 0 overdue amount. I want them to close my account and refund my money back. I have been with this people for long but now I am done I will never buy anything with them again.