Billing issue

I have a 2years unlimited ADSL contract with Telkom thats is going to expire in August this year. It was initially for R800 at first then it was brought down to around R650 due to the delay of the Fibre line that I have app**** for last year June and still waiting for it today. Then all of sudden I got my January and February statement stating that I must now pay R1305. 81 and all I'm hearing is that the did bill me for my telkom line in December that is one my bill is going up. So how is that my problem. Telkom made a billing mistake not me and how can a bill be double just like that without any notification. Even their call center agent can't justify it... Telkom must just cancel both my contracts cos they have a **** customer service.