Help! Vodacom is harassing me about upgrading!

I am pulling my hair out over here. I am being harassed over and over again by Vodacom, because apparently it is one of the seven deadly sins if you decide to not upgrade when the computer decides it's time. How many times I have asked agents to stop calling me, but no, they keep coming back. And the last few were quite aggressive when I told them to leave me alone. It is a free country (in theory anyway)! If I don't want to talk about upgrades, I don't have to explain myself! I phoned Vodacom out of desperation now, and after almost 12 minutes, I was promised that it won't happen again. Pffft, I will believe it if I see it. LEAVE ME ALONE VODACOM! I will upgrade when and how I choose to do it.