Not a mobile number. It's my land line work number that is posted / listed on hundreds of sites, search engines, and directories. Don't really want to get a new phone number.
One thing that has anecdotally worked in the past is putting the three-beep disconnect tone at the start of my answering machine message. That
do-doo-DOO series of tones. You apparently don't need the rest of the "I'm sorry..." message, you can follow it with your own "Anarchy99 can't get to the phone right now, please leave a message at the beep" after the two second do-doo-DOO. The rumor is that auto-dialers and spam calling computers will disconnect and remove your number from their database upon hearing the tones, their computers don't listen to the voice part of the recording. Humans, though, might be initially confused for a few seconds but they'll hear your voice and continue with the call. Do it for a week or two maybe and switch back and see if calls are reduced.
Otherwise, yeah, some kind of spam filtering/forwarding might be necessary.