Unfortunately, these are probably what they call "SPOOF" numbers. The caller is probably calling from a real number but using a spoof application to hide the real number that shows up on your phone. What you see is the spoof number. That's why in some cases you call back and the number is disconnected or not in use because they are not using real live numbers. Unfortunately there is not much you can do about it. Even if your number is listed on the do not call list. The best thing to do is not answer a number that you are not familiar with. Google it to see if it is a valid number or not. Don't pay for telephone look ups. You can pretty much figure out what the number is with google. Block the number. But they will most likely use another spoof number and call back again. I get 2 to 3 spoof calls a week. Best protection don't answer a number you are not familiar with.

Just called me. I didn't answer and no voicemail. I sure hope it doesn't keep calling me like all these other people!

Call from this number came in on my cell phone AND at my work within a 24 hour period!  "Congratulations!  You have been selected to receive a free cruise!"  I hung up on them both times.

Gawd, I hate telemarketers.

Some type of "free cruise to the Bahamas" scam. I only classify it as a "telemarketer" very loosely. I hung up and blocked the number as soon as I heard that. I only answered because I thought someone I knew might've just gotten a new phone.

Unrecognized number, did not answer. No message left.