There is a free call blocking service that is not available on every phone system. The filter prevents me from posting it or the thread link here. Think No More Robot. Put a play on those words and you will find it. As an alternative
Call Blocker
You need to buy a standalone call blocker, call blocking phone, use your carrier’s call blocker if they offer one, or download a free call blocking app for smart phones. For conventional cell phones, assign the number a letter like “z” and make no ring. You may also need to have your carrier increase the ring time to avoid having them leave a message on your voice mail.