Probably time to buy a call blocker device, app, or phone.
Google "call blocker" to see the various types, and find one that best meets your needs.

They don't help if you don't have the number to block.    This foreign scammer uses phantom CID numbers and the calls originate outside of the USA, thus the FTC has no jurisdiction.

I have my call blocker set at "Universal block" where everything is blocked except those on my exempt list.  I can set it to block by selected area codes or all area codes.  Also,  it will block any call that has "Unknown",   "out of area",  "Private"  and crap like that.  We keep every known relative or acceptable neighbor on the "exempt list".    It may not work for many people but works great for us.  Any business or anything like that can put it in the mail if it is important enough.

Slim is referring to a mechanical device that you can purchase and attach to your telephone.  Most work great.

Newest models I saw when I looked them up also cover unknown and private names and numbers..