Eugene's observations

1. You receive a phone call purportedly from a local number (CLI can be faked)
2. The voice on the end introduces themselves and the company they supposedly work for (thieves lie)
3. They then ask: "Can you hear me"? or "Are you there"?
4. Your answer is recorded
5. If you say "yes", your response will be edited to make it seem as though you have agreed to a verbal contract for a major purchase.

I know that people think it's impolite to hang up, but it's a good strategy. If you don't recognise the number, don't answer.   A genuine caller will leave a message.  At the very least, don't speak at all until you are absolutely certain of the caller's bone fides. 

If you are lonely call a genuine person.  see  
http://www.ageuk.org.uk/health-wellbeing/loneliness/  
http://ben.org.uk/news-hub/beating-loneliness/