I get a lot of these calls, and I figured out the pattern very quickly. Since I don't happen to know anyone with the same areacode/prefix as my cellphone, I just let all these calls go to voicemail, and none of them ever leave a message. (My area code is an overlay area code that has mostly mobile numbers.)
I do too! It's very frustrating, to the point that I've considered just getting a new phone number. The problem being I've had this number for >10 years and like the idea of an old high school friend being able to reach me without Facebook. Someone online suggested I make a complaint to the FCC but it went nowhere. I never pick up anymore but it's still annoying.
I wouldn't expect that getting a new phone number would help. I'm guessing that these scammers sequentially call all the phone numbers in an area code rather than targeting specific individuals. (If they were targeting me, they'd probably stop wasting their time after the hundredth time I didn't answer their call.)