Getting the same calls every day. If you answer it hangs up

I have had the same if i answer it hangs up and there has been no msg either

(03) 9223 5405 this number has rung and not left message or if I answer, just hangs up. Rang it back to see who it is, National Parks and Wildlife about a buddy something program. Maybe trying to get sponsors? How do we ask them to stop ringing if they aren't there when they ring and don't answer when you ring?