Being Billed for something which has no been in use.

My Fixed line service, I have been billed for a service which was in no use(line has been suspended) for the past 3-4 months, Can not be charged for something which had not been used for the past 3 4 months with no service up until now there is currently no service, please reverse charge of R798.56. keep going to the call centre they have people who can't even assist as well as they team leaders suck pathetic ******* service, Trying to cancel a service but can't even do that when you get billed for things you don't even use.