Do a search on call blocking devices and phones.If its a cell phone, there are free call blocking apps out there including trac & straight talk.
http://800notes.com/forum/ta-5d4e343675a5629/call-blocking-devices

http://800notes.com/forum/ta-de071afa5bd5041/dangerous-new-trend-in-irs-scams
http://southwickpolice.com/irs-scam-swatting-incident/

http://www.irs.gov/uac/Tax-Scams-Consumer-Alerts
http://www.treasury.gov/tigta/contact_report.shtml
http://800notes.com/forum/ta-8c2f64bf2b91fa5/irs-warns-of-telephone-scam

http://bigstory.ap.org/article/4b849c65e54346 ... leader-irs-scam

Report the Calls to the real IRS here:
• Report the incident to the Treasury Inspector General for Tax Administration at 800-366-4484.
• You can also file a complaint with the Federal Trade Commission at FTC.gov. Add "IRS Telephone Scam" to the comments in your complaint.

To file complaints on Foreign company's and scams:
Read up on it here:
http://800notes.com/forum/ta-d20d86fdc3e145c/reporting-international-scams
https://www.econsumer.gov/#crnt
eConsumer.gov: Report Your Complaint
E-mail: [email protected]