Spam Calls With No Answer

I have been receiving calls for about 3 weeks now from a caller with ID "Standard Bank Mobile". On average I get 3 calls from them daily, but whenever I answer, there's silence on the other side and they just hang up. They also call using different numbers. I cannot get rid of this and it is starting to get quite annoying. Let me list some of the numbers here: +***2 +***8 +***1 +***0