Call blocker is your best bet.   These people are scammer/extortionists located in India and beyond the reach of US law enforcement.  

See:  http://www.irs.gov/uac/Newsroom/IRS-Warns-of-Pervasive-Telephone-Scam

Have received many messages, called back today officer Eric foster got nasty , he can speak English fine when he is being treating and vulgar.  It is a scam.

Got the same call and number. I called him back, questioned his creditability, and demanded details. He got scared and hung up on me! REALLY?!!

Said they were calling for the Internal Revenue Service Department on a tax audit.  It's a scam and do not call them back.  The caller used broken English and an obvious script.