Billing Error

How is it possible that I owe Dstv R1388 when it is a prepaid service??? I am on Compact Plus and my subscription is R559 and thats including insurance! I tried to resolve this over the phone with no success and I was advised to go one of their walkin centres which I did (umhlanga). The service I received there was appaulling to say the list, the guy who assisted me could not explain why it is that I was owing them that much but he did say they had a system glince which is why it showed I owed them that much and I should pay the amount owing! He even went as far as calling his team leader who also said I should pay. I have never missed a payment! I paid the R559 that I am meant to pay but its still showing I owe them R1388 the issue is still not resolved! The ****** team leader went as far as saying they can make arrangements for the balance owed but my question remains how does your system make an error and I am expected to pay for your system error as a consumer??????? I need this resolved ASAP!!! I am disgusted to say the least!!???