This company First Alert Security endlessly robo-calls my cell number with no way to opt out of receiving these calls. Several calls each day with rotating telephone numbers. I am on the no call list
If this is a Home Phone they called, get a Panasonic KX-TG6512 (about $55 from Walmart on-line). This portable phone is GREAT in every way and allows you to program and block up to 30 numbers. Then the phone will ring once and record the number of who it was. Then you can check it on "Who Calls Me?"
It's time for someone to invent a box to install on your phone that checks this site for bogus numbers. Once a number has been reported several times by credible posters, the box would prevent that number from ringing your phone. Maybe the box is a Raspberry Pi.
There used to be a box that would answer the phone and ask the caller to input a four-digit code. If the caller did not have to code, the call was transferred to the answering machine. The phone never rang. Unfortunately, the company went out of business before I could buy one.
With so many people pulling the cord and using cell phones for their only telephones, I doubt there will be a technology solution. The cell phone companies and device manufacturers control the technology. Even AT&T call blocking on a home phone only works against other AT&T home phone numbers. That's useless.
I've also got a Panasonic phone and do the same thing. Block harassing callers and then check this site to see who's calling me. I grin every time the phone rings once and then blocks the caller. Only problem is I could probably block another 30+ calls in addition to the 30 numbers I've already blocked. Are you listening Panasonic?