This is an invalid area code.  I have had ten calls in the last two days, all of them with Invalid Area codes.  Then I noticed that a lot of them have the same last four digits in the phone number, sometimes using a different exchange code (876 or 768 or 999 for example).  Most of the time the exchange codes are also invalid.  I do not understand how this cannot be controlled.  But that is a different rant!  Anyway, what I am doing now is this:

-- Phone rings, I look at the number on TV screen, if it looks phony, I immediately pick up the receiver.
-- Take the phone (quietly) into my back bedroom, lie it face down on the pillow, and leave the room.
-- Once I hear the signal that sounds when your phone is left off the hook, I go back in and hang it up.

This will only work if there is absolutely NO background noise going on when you pick up the phone.  I mute my TV, make sure there is no street noise, and that's why I hide the phone in the pillow.  Doing this after the phone rings only once or twice (you'll learn to be quicker with practice), then it will give the impression that it is a non-working number.  They'll probably try a few more times, from different numbers usually.  But after twelve calls in two days with this treatment, the calls have stopped ... for now.

The minute you say a single word or yell into the phone or use a whistle or other noise device, they know it is a legitimate, working phone number, and they will keep trying.  One thing I have a lot of is PATIENCE.  They can keep calling; I will keep using this method.  We'll see who lasts the longest. I'm betting it is ME.  Try it.  

Then I come in here to see if others are bothered by this number, and I leave this message for everyone one else to see.