Silent calls from telemarketers wasting my time

I've been receiving 2-3 calls a day from ***. The person on the other side would just be in total silence (as if muted). I've managed to ascertain that it is from a Vodacom call center / telemarketer. I could be wrong though, and if so I apologize. Is there a way to stop them from getting benefits for the amount of calls and rather rewarding them for sales? This is really getting on my nerves. I don't have time for this nonsense.