This is not a legitimate call from the IRS.

Please see the following press releases:
http://www.irs.gov/uac/Newsroom/IRS-Warns-of-Pervasive-Telephone-Scam
http://www.irs.gov/uac/Newsroom/IRS-Reiterate ... -Telephone-Scam

Since this individual is impersonating the IRS you should also report it to the Treasury Inspector General for Tax Administration (TIGTA). You can send an email to Complaints@tigta.treas.gov or file an online complaint by completing their "Online Form" located on their website, http://www.treasury.gov/tigta/contact_report_scam.shtml

Please visit our "Report Phishing" website (http://www.irs.gov/uac/Report-Phishing) and click on "Complaint Assistant". This will allow you to file a complaint with the FTC and identify the complaint as an IRS complaint.

Alternatively you can file a complaint directly with the FTC by visiting http://www.ftccomplaintassistant.gov.

Whether you use the IRS link or file the complaint directly with the FTC, add "IRS Hostile Call" in the Comments section of the complaint.

Individuals who have been victimized by this scam and have provided one or more Green Dot MoneyPak numbers to the scammer should also notify Green Dot directly at 800-473-3636 to report the scam and open an investigation.

Regards,

phishing@irs.gov
Online Fraud Detection and Prevention (OFDP)
Internal Revenue Service
United States Department of the Treasury

report any calls from District of Columbia 202-241-0331.

locate this number and report it: 202-241-033. pretending to be an IRS investigator, heavy eastern indian/pakistanian?? accent, offensive language.

Here is a story from FOX 13, Tampa Bay, Florida about these calls.  It's the best explanation I've found so far of these calls as well as what to do when you receive one and to whom to report the call and how:

http://www.myfoxtampabay.com/story/26206940/2014/08/05/phone-scam

IF YOU READ NOTHING ELSE IN THIS THREAD, AT LEAST FOLLOW THE ABOVE LINK AND WATCH THE VIDEO CONTAINED IN IT.