They're called ROBO calls for a reason. It's a program that calls (for instance) your number, then add a digit for the next and so on. When you answer the call, there's a bit of a delay for the person on the other end to pick up the call from their auto-dialer. If you answer a call from these scammers, you are only confirming you have a viable number. They will share (or sell) your number to other scammers. ABC's 20/20 had a great report on this problem. Simply don't answer. if you have a call blocker, use it. If the caller is legit, not only will they display their name and number, but if you don't answer, they will leave you a message. Scammers don't go by the rules, so don't blame the DNC list. They can make any number appear on your CID and chances are they're calling outside of the country.
On do not call list this is a business ph don't call it it if it doesn't pertain to our business and best we can't accept any kinds of gifts against Manheim policy
Answered and heard robot voice: "This is Allison from the Warranty Department. Can you hear me OK?" (I didn't reply.) "This is your final warning that your warranty will expire soon." (No info provided on what warranty or product supposedly is expiring, so I hung up.)