They called again a few minutes ago. Since I added them to the block list already, it went straight to voicemail but they didn't leave a message. Glad I have a smartphone.

The Do Not Call Registry is for the birds.  You can submit a number and complaint but they do nothing because they are not affiliated with any level of Law Enforcement of Investigative Agencies.

Apparently you do not understand how that works. The complaints are accessed by all agency's.  The DNC isn't a call blocker and can not protect you from the illegal callers, extortion scammers, foreign country's and frauds. Criminals do not obey laws simply said.    They use spoofed numbers which make it hard to track them down.. it takes time to do this and many subpoenas for call records.

http://800notes.com/forum/ta-c3355f57425c0d5/ ... alls-to-the-fcc
http://consumerist.com/2015/07/22/45-attorney ... lock-robocalls/
http://800notes.com/forum/ta-c5c7e69f0670886/ ... -spoofing-calls
http://800notes.com/forum/ta-c46b87360deec56/ ... -unwanted-calls
https://www.ftc.gov/news-events/press-release ... ainst-political

Do consider getting a call blocking device or phone..  You can google them and many are around $40.00 or so.If its a cell phone, some already have call blocking, if not, there are free apps on the web that will work for some. You can google this. If you have a smart phone, there is a free app called call control. Iphones appear to have apps also. Another one is called Mr. Number.

Report your callers here and not just to the DNC itself:

https://www.ftccomplaintassistant.gov/#&panel1-1
https://consumercomplaints.fcc.gov/hc/en-us
https://complaints.donotcall.gov/complaint/complaintcheck.aspx?panel=2

By State DNC lists:
http://800notes.com/res/DoNotCall.aspx

To file complaints on Foreign company's and scams:
http://800notes.com/forum/ta-d20d86fdc3e145c/reporting-international-scams
https://www.econsumer.gov/#crnt
eConsumer.gov: Report Your Complaint
E-mail: econsumerwb@ftc.gov

http://www.stopfraud.gov/report.html
http://www.fraud.org/

And here are the links to read and understand what the DNC's are, what they do and what they do not.

By State DNC lists:
http://800notes.com/res/DoNotCall.aspx

http://www.tcpalaw.com/
http://www.consumer.ftc.gov/articles/0108-national-do-not-call-registry
https://www.donotcall.gov/
http://www.ftc.gov/opa/2008/04/dncfyi.shtm
http://business.ftc.gov/documents/bus27-complying-telemarketing-sales-rule
http://business.ftc.gov/documents/bus27-compl ... -rule#DNCrights

They called me again. Phone blocked it and they didn't leave a message.

Call at lease 4 or 5 times in one day,and it is very annoying.