I've had 6 calls from this number today but since I don't answer calls from numbers I don't know, I have not answered. Another site says this is a spam number.

Number keeps calling, doesn't leave a message and hangs up when I answer.  Adding to the blocked list!

Same here!  It's harrassment !  It's an automated message about student loan forgiveness.  I am not only getting calls but texts as well.  When you call back, it gives you an option to be removed from their list.  But guess what ? You will STILL gets their calls !!!  I can't get them to stop.

To stop them use a call blocking device/phone (or call blocking app for your smart phone). It will also stop those groups that are exempt from the DNC List. They're available online and start around $50 or so. http://800notes.com/nb/search?q=call+blockers
Also take a look at this: http://www.wikihow.com/Block-a-Call
Do not answer unknown calls and do not call them back.

called three times in a row without leaving a message
hung up the first time (i answered)