Cancelled DSL, but i am being billed for a month!!

I have had enough of telkom, I have had continuous problems since i had the DSL put in. I would sit next to my router and no internet connection!! i have tried contacting them numerous time no luck. I then decided to cancel DSL a few months ago but the lady assisting me (I also put them on Hello Peter mind you) convinced me to give them a chance to come out and fix my problem, but still no end to my problem. I then did not pay them hoping someoen will call me but noone even bothered all I got was a sms saying they handing me Over to lawyers!! fine i paid them up to date and cancelled my DSL (when i installed it i was told I can cancel at any time) I get my bill and they are billing me from the 03 December until 03 January! and my line was put off! why must I pay a whole month for a service I am not able to use, a service I was struggling with for more than a year! I refuse to pay for a month because that is not what i agreed to. I call the billing department and guess what im told, mam you need to go to a telkom strore!!! to do what exactly?? I refuse to pay for a line I cancelled and is put off, I suggest Telkom start paying more attention to their customers.