Bad service

I have a problem with dstv this month I paid 300 rand and they told me that im still owing 229 of late payment not understand what they mean because for july and August i paid close to 600 rand and I called them they said its for two decoders while i only have one decoder that I'm using now what im asking is the they owe me two months why they do not take from that money they owe me and how can they charge me 229 for late payment.and i know that my insurance is 23 rand now i have been told it is 35 rand they don't notify people when it has increased.