Thats not true.  Illegal telemarketers are just that, illegal.  When you register your number with the FTC for the DNC, if these company's do not abide by it, its illegal same as are the spoofed numbers the illegal ones tend to use. its a law the frauds, scammers and other illegal callers love to break. They do need reported.. The DNC is a database of complaints all agency's use. Charities, Political and some survey's are exempt from the DNC. 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:  [email protected]

To file complaints on Foreign company's:
eConsumer.gov: Report Your Complaint
E-mail: [email protected]  

Do consider maybe getting a call blocking device or phone.. You can google them and many are around $60.00 or so.

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