DSTV has lost my billing details. overcharged

Dstv changed their billing systems at middle of this year. I moved to Cape Town and switched off my subscription via self service. I had a months subscription on premium and pvr services. Ie I was a month in credit. I have requested this billing information from dstv in order to get clarity on amount of credit. Dstv has said they have no records pre their new system. On mylast call , ayanda claimed dstv to have credited my account with R300. There is no reflection of this credit amount on my bills. If anything they chargedme anadditional R300. And still no details on my previous billing pre their system change. I've made 3 requests via telephone. This is now the 4th request - via hello peter. Due to the poor billing and service I have chosen to downgrade my package. .. only to be told that they are having technical issues. I must try next month. Sounds very fishy to me...Please assist