I’ve given up on spam flagging and blacklists and anything else that requires effort and moved to a white list. All previously unknown inbound caller IDs to my system must prove they are human, after which they get white listed. All outbound calls are automatically white listed: Of Robocalls and Whitelists
Spammers are starting to evolve, over the last several months a few robocalls have gotten through. If it gets worse, I will be adding a random captcha.