When you receive a call from an unknown number, and they ask to speak to Mr/Mrs 'so-and-so'. The first words out of you should be "Who is calling please?'. (Please is optional, but you can be nice at first). If they won't say, or you don't like what they say, Hang up! Don't argue with them, don't ask to be put on a DNC list, just hang up. They're phishing for information.