Won't cancel service

On 9 Oct I sent a cancellation form to Telkom. They said would take 21 business days. On 26 Oct I got an email sayign they acknowledge receipt of my cancellation and it would take 21 business days. Surely Telkom's delay in processing emails shouldn't become my problem??? On 13 Nov I noticed that our landline was no longer working. Yet we still continue to be billed - why??? I have tried calling and am on hold for half an hour or more and even then no-one can help. I am tired of receiving sales call to upgrade my service - the service is supposed to be cancelled!!! And then to top it off the agent I was dealing with decided to hang up on me because I refused to accept that the manager is always in a meeting and may or may not call me back!