All they have to do is plumb numbers into a computer or robo dialing machine. However, google your name and number, any place such as spokeo that shows up, make them remove it.

http://800notes.com/forum/ta-ca7cb90a6ac5c31/ ... eal-your-logins
http://800notes.com/forum/ta-9b593c6d671798c/ ... sed-to-scammers
http://800notes.com/forum/ta-c5016ae94e29b44/ ... oyment-benefits
http://krebsonsecurity.com/2014/04/u-s-states ... ch-at-experian/
http://800notes.com/forum/ta-a55d53405a192ce/ ... alware-campaign
http://www.nytimes.com/2014/08/06/technology/ ... tials.html?_r=1

For 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. For tracfone & straight talk:

https://play.google.com/store/apps/details?id ... .tracfone&hl=en
http://extras.straighttalk.com/en
http://www.youmail.com/home/carriers/straight-talk/block-number
https://www.straighttalkwirelessforum.com/viewtopic.php?f=6803&t=55006

For text messages: forwarding any text message spam you get to the short code  “7726,” which spells “spam” on most phones, to alert your network operator to the abuse. ATT won't accept 7726 But they will accept BLOCK and return a message that the web site is blocked. forward the texts to 7726 or BLOCK, depending on your phone carrier.
http://www.att.com/esupport/article.jsp?sid=KB115812

Report your callers here, not just to the DNC alone:

https://www.ftccomplaintassistant.gov/#&panel1-1
https://esupport.fcc.gov/ccmsforms/form1088.action
https://complaints.donotcall.gov/complaint/complaintcheck.aspx?panel=2

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

FCC Abandoned Calls Complaint form:
http://www.fcc.gov/cgb/consumerfacts/1088D-R.pdf
email:  fccinfo@fcc.gov