Calls during the day and evening.  Annoying

I believe this is the NRDC

These people call nearly every day.  Today is Sunday and we received a call @ 6:35 pm.  They don't leave messages and we don't answer the phone.

My caller ID says NRDC 323 330 1435.  These calls are at least two a day. No messages left on answering machine. When I answered the  phone noone was there.   I called the number back, a recorded message said I had reached the National Resources Defense Council and to hold for a representative.  I finally gave up after 24 rings.  Who are these people?

This number keeps calling day or night as late as 9 P.M.  It is very annoying.  We are on the NO CALL LIST and I am fed up with them calling all the time, 2 - 4 times a day/night.  HELP?