Billing for services never recieved

I upgraded my Telkom adsl from a uncapped advance 4mb/s to a uncapped premium 10mb/s line in November 2014, from that day I had problems of adsl line not syncing more than 1mb/s, in January 2015 a field technician sorted the problem out for me and phoned me while I was at work to explain to me that my area can not receive 10mb/s speeds and telkom downgraded me back to a 4mb/s uncapped advance package and my adsl line is working perfect on 4mb/s. Telkom sent my my bill every month to my email were they only charged me for uncapped advance on a 4mb/s line and I was happy and payed them according to bill and I was only receiving 4mb/s and this I confirmed with the telkom sales department and technical department from DEC 2014 up to date. in November 2015 I receive a Bill with an amount of R4146 stating that I have uncapped premium from December 2014. I did dispute the error and telkom rejected it twice already, today i disputed the account again, with every dispute you have to wait 6 to 8 weeks to resolve and they want to cut my services were I feel this is unfair. why do I have to Pay for services I never received.