Cancellation

I have been trying to cancel my internet line for about a year and a half. But they keep billing me. Now they have given me over to attorneys because I dont pay for the service that I have tried to cancel. It is mind boggling, ive called, ive mailed, ive even been in the telkom shop. I dont know what else I need to do anymore. Why do I have to pay for a service that they are too lazy to cancel?