Harassing Phone Calls

Vodacom has been harassing me with calls. Trucaller shows the number comes from Vodacom upgrades. When I answer the call, it is quiet on the other end. I block them and still they continue to call. I've tried calling the customer care centre but I can't get to a consultant. Please note this on my profile Vodacom. I am not interested in an upgrade and I am not interested in renewing my contract. Please stop calling me.