Do a search on call blocking devices and phones. If they change numbers but not the area code. you can block them by area code which works even better! For a cell phone, there are free blocking apps out there even for trac and straight talk.

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

Federal:
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

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

To file complaints on Foreign company's and scams:

https://www.econsumer.gov/#crnt
eConsumer.gov: Report Your Complaint
E-mail: econsumerwb@ftc.gov
http://800notes.com/forum/ta-d20d86fdc3e145c/reporting-international-scams

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

Same Credit People that have been calling me for months saying that they will lower my interest rate . . . they always change numbers they call from. Screw them.

When answered, the caller message is that I recieved the wrong  extension and then hangs up.  Assume it is a telemarketeer of some type.  Call blocked and number reported to AT&T as well as local Sherrif's for follow-up and action as necessary.

Credit card scam !