Unfortunately no one has come up with a viable solution to these vermin yet. I have considered Black Flag insect repellent or Agent orange, but I'm not sure that will get er done.
The purpose of having your number listed with the DNC registry is to get your number registered with the FTC. That list to required to be purchased by Legitimate and Registered with the FTC Businesses, maintained and kept up to date. It does not monitor, screen, or block unwanted calls for anyone. It has no means or people to mechanically block the over 1 billion 500 million calls placed in the USA each and every individual day. It is not a Department of the Government with an army of employees and huge budget. It is a section within the FTC, whose intended purpose and only purpose for creation is simply to maintain and provide this List for those Legitimate and Registered businesses to limit telemarketing calls to those who are registered.
It is not a law enforcement tool. Your caller is a scammer who does not purchase this list and of course they are not registered to purchase it nor would they if they could. They can, just like every other telephone in the world, dial any other telephone in the world and ring that phone. The DNC list does in fact work or else all of those millions of legitimate and registered with the FTC American businesses who are now NOT calling you because they honor the system, would be ringing your phone 24 hours a day. But they don't because of the list.