You can choose to reject it, which is what my Google Phone app does by default when I block a number, or accept it to instantly hang up. I just chose the reject option, most calls stopped completely after a couple of weeks. I do not use voicemail, so not sure how it interacts with that. The app also has an option for a subscription (as in you just insert a link) to an ever updating list of spam numbers, but I just went with not my contact = no business calling me.