I simply refuse to answer number witheld calls - that means that the caller has deliberately chosen to hide their number & for someone calling me, there's no good reason for doing so.

You may be able to setup your phone to simply ignore withheld number calls, without even ringing. If someone has a legitimate reason for calling, they can display their number & given that your caller doesn't even leave voicemail, then they're not worth spending any time or stress on.

BTW, I'd actually advise against pick up/hang up - that confirms that they're calling a valid number & may set you up for further calls. Same thing for blowing an air horn down the line at annoying phone pests - doesn't work, because phone systems will automatically clip signals beyond a certain volume.