That's because most of these people spoof their numbers and just use random numbers. Sometimes they'll even use legit business numbers. I had a number call me one time and when I called the number back, it was a business owner explaining to me that he has been getting calls all day and hasn't called one person.
They called my very private cell phone number at 11:18 AM PDT on 6 October 2016. The caller ID said "Delaware, PA". I did not answer. They did not leave a message. My phone numbers are on the Do Not Call list. I will report them to DoNotCall.gov.
Never call them back, not even from a blocked phone. They have ways to unmask your phone number even when it is blocked.
They just called me on my cell. I didn't pick up, just blocked it on my iPhone. Everyday I get calls from across the country, weird cit names too. Whenever I call them back from a blocked number, it is always a DISCONNECTED number, fraud.
Accidentally picked up without checking who was calling the other day. Now I'm on a list of verified numbers and the robo-spammer keeps calling multiple times a day!
Caller ID says "Delaware, PA". I did not answer. They called back in about 3 seconds... literally. It was three seconds later when they tried again. BLOCKED.