Got a call from this number however there was no message left.

It's an Obamacare-related call from SEIU, a union striking against Affordable Care Act. I don't understand why it is legal for them to robo-blast calls.

http://washingtonexaminer.com/seiu-unionists- ... article/2536458

I got a call from this number, and the caller keeps spamming my phone. However, when I answer, there's no one there, and they hang up after 11 seconds into the call

Since all the different call spammers monitor the various complaint phone call sites, here is my response to them;
Just a note to all the solicitors, charity organizations, and political groups that continue to call using a caller ID of "out of area", "local caller",  "toll free caller" and the like, you will be forever call blocked until such time as you choose to show an accurate caller ID showing what organization you represent. So, even though you may have products, services, or information that I might use, you will never reach me as long as you continue to employ dishonest tactics!

They called and did not leave a message.