Almost all the illegal calls are from spoofed number. Those are hard to track down. Some are from foreign country's and of those, some of those can cost you big time to call back. ROT, do not answer numbers you do not know and do not call them back.
phone spoofing explanation
http://en.wikipedia.org/wiki/Spoofing_attack
http://www.fcc.gov/guides/caller-id-and-spoofing
If your cell doesn't have call blocking, then google free call blocking apps. Mr. Number is one such for cells. Maybe one will work for yours. If you have a land line, consider maybe getting a call blocking device or phone.. You can google them and many are around $50.00 or so.
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]