Telkom Frustration!!!

There should be zero rating option here...how is it that a company like Telkom can get away with offering the *********** service that they do and still be in business? We have been trying to cancel a business line that is no longer in use. We have submitted all the necessary info that they require, but the only response we get is that they acknowledge our request and and agent will be in contact, which doesn't happen. They only give you an option to cancel online via e-mail and not through one of their outlets, but it doesn't appear that you can successfully do this. What are people supposed to do? I have heard many accounts of the same stories with people not being able to cancel. We settled the account in March and have now still received an invoice in May to pay for a line no longer in use. Surely we have rights?