Well, Fed Up, if you read these boards with any regularity, you'd know. There are dozens of ways for these people to "get your number", but the biggest one is that they simply auto-dial all possible numbers. There is no way to "get off their list", the best you can do is buy a call-blocker and add them each time a new number calls. Most of these scammers are in India or other foreign countries, so it's really difficult and expensive for the US government to go after them. Mostly the government has bigger fish to fry.
I just simply don't answer calls unless the ID is someone I want to talk to. Everyone else gets the voicemail, if it's important, they WILL leave a message. If they leave a message that isn't important (like this or political robocalls), it's easy enough to delete. Don't get you shorts in a knot over something that's easily solved. We get two or three calls a day from numbers like this, I never answer, and when I look them up, it's always scams like this. But the more you talk to them, the more calls you'll get.