Over pay on Account, now arrears

i purchased a deep freeze from this compay principle debt was about 5900. my repayments is supposed to be 365 rand per month. so i decided to repay 500 oer month to pay it off quicker, to my dismay they are not taking the extra money off my account it is being put under heading arrears with a positive balance. my positive balance is now about 900 rand. this month i payed 350 rand. and guess what happened? Lewis phoned me to tell me the installment is short 15 rand. i told the woman on other side that my account is in positive and not arrears. she said she saw that but the system wont allow for them to use that money i must put another 15 rand into it for this month. Now my question is this- WHO ARE THE INCOMPENANT PEOPLE DESIGNING THESE SYSTEMS. <br> <br> I WONT BE BUYING FROM LEWIS ANYMORE EVEN THOUGH THEY PHONE ME EVERY WEEK TO OFFER ME CREDIT TO THE VALUE OF 45000 RAND. because there system is flawed. it is only there to make money on interest, does not matter if you want to pay back faster.