Or they are also possibly calling over the internet with a VOIP service. This can also generate telephone numbers in the caller id that can't be called back because they are not valid telephone numbers.
Called 3 times in a row, each call was within 5 minutes of the previous one. No message. Nothing on the caller ID except "Unknown". Very creepy feeling like I was being watched screening my calls.
if you try to call it back it says the number is incorrect so how are these people whoever they are calling us from a number that isnt even working.......When the call comes through it has a additional 2 0's on the end
They are calling you from a working telephone number...but they are transmitting false caller id information to hide their identity. It is called caller id spoofing.
Or they are also possibly calling over the internet with a VOIP service. This can also generate telephone numbers in the caller id that can't be called back because they are not valid telephone numbers.