Telkom Dispute

I have a internet connection with Telkom with I took out 18 months ago. With having a problem with the connection in September I discovered that Telkom had never upgraded my line from a Dsl2line to Dsl4 line that I was paying them for. They than agree to compensate me for the error R6. 06 for every month I was without the correct line I am demanding half money back for half the service they provided me with but have no joy from them can anyone help me to resolve this or know who I have to contact to get this resolved Thanks