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.
You may also wish to file a complaint with your local LE and also with your phone service provider.
http://800notes.com/arts/I2neMkbUAAo/where-to-report-phone-crime
Report your callers here, not just to the DNC alone:
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.
By State DNC lists:
http://800notes.com/res/DoNotCall.aspx