Upgrade calls unnecessarily when the Upgrade is not due.

I upgraded my cell phones less that 6 months ago, and now Vodacom keeps calling me to tell me I am due for an Upgrade, do they not keep records of their customers when the customers upgrade their cell phones, and not bug me every 6 months to tell me I need to upgrade my cell phones, as I believe you only need to upgrade every 24 months, Vodacom is the worst service provided I have experienced and very costly.