called and left no message caller ID said Local Call

Someone calls several times a day from this number.  We don't answer and it goes to the answering machine.

also called no message left

Called 4 times today.  Caller id says local call.   Do not leave a message.  Called once yesterday,

This number calls exactly four times every day.  I answer and say "Hello."  They say nothing.  I say "Hello?" again and they hang up.  Every time.  Sometimes as soon as I hang up the phone, they call back immediately, also with silence and then hanging up.  VERY annoying and very frustrating!  WTF?