Vodacom, persistent rude tele sales agent calls

I am disgusted with the rude and belligerent attitude of tele sales agents acting on behalf of Vodacom. I recently received a call from an agent who proudly announced that they were not selling me something, who then proceeded to tell me I had to sign a 24 month contract when I declined, the agent felt it necessary to forcefully question my decision and while I was responding to hang up the call. In the first instance I do not recall asking to be contacted for marketing or sales purposes, and I am usually pedantic especially about contact via my mobile phone. This is not the way to retain customers.