This is a magicJack number.  From phonevalidator.com :

Phone Number:    202-241-2099    
Date of this Report:    March 22, 2014
Phone Line Type:    LANDLINE
Phone Company:    YMAX CORP -- POSSIBLE MAGICJACK VOIP

YMAX Corporation is a wholly owned subsidiary of magicJack VocalTec Ltd, a company that makes most of its money selling magicJack devices and phone service.  YMAX Corporation provides phone numbers that are used to connect magicJacks to other telephone companies, so that magicJacks can make and receive cheap calls anywhere there is Internet service.  One location where they have a large pool of telephone numbers to assign is Washington, DC., but you can choose any number they have in any location in the US for your magicJack, just as you can choose any area code for your cell phone.

The same things that makes magicJacks so useful for legitimate users also makes them useful for scammers, along with the fact that they are very difficult to trace.  However, magicJack VocalTech Ltd. has been cooperative, at least in some of the reports I've seen, with law enforcement when their records have been subpoenaed by law enforcement.

I suggest you report this number and fake IRS agent as follows, according to the information found on their web site:

>>>>>
"If you get a phone call from someone claiming to be from the IRS, here?s what you should do: If you know you owe taxes or you think you might owe taxes, call the IRS at 800-829-1040. The IRS employees at that line can help you with a payment issue ? if there really is such an issue.
If you know you don?t owe taxes or have no reason to think that you owe any taxes (for example, you?ve never received a bill or the caller made some bogus threats as described above), then call and report the incident to the Treasury Inspector General for Tax Administration at 800-366-4484.
If you?ve been targeted by these scams, you should also contact the Federal Trade Commission and use their 'FTC Complaint Assistant' at FTC.gov.  Please add 'IRS Telephone Scam' to the comments of your complaint."
<<<<<
From: http://www.irs.gov/uac/Newsroom/IRS-Releases- ... Scams-Lead-List

You might also want to add that you believe the number calling you is a magicJack number.

This guy dons a South Asian accent (Indian, Bengali, or perhaps Pakistani), says he is from the IRS, and claims there is an affidavit against you for fraud. My husband knew immediately it was a scam, and had a great time taunting the douche-bag with challenging questions and smug comments - which really got under this guy's slimy skin. A few minutes later he called my mother-in-law, but her home health-aid didn't buy into the b***s***. Don't believe the call, and NEVER answer any questions involving identifying information, no matter what the nature of the call is.

His name is Sean Watson. It's crazy!!! all this things that you guys said is exactly what he said to me. Is this really a fraud? Is there anything that I have to worry about?

I wish there was a way to catch these thiefs who go about conning people. I am an indian myself and am ashamed to admit that these are people with indian accent who are calling and putting charges of tax fraud on law abiding citizens

This man called me with an Indian accent, 3 times in 5 minutes, basically rambling on and on about some legal case. He ended the call with "If you do not return the call [REDACTED], or I do not hear back from you, all I can do is say 'good luck' may god help you. Goodbye."

This man called me today and stated the same thing as the above person about a fraud comitted. Was unprofessional called three times left three messages and said "may god help you"

A guy from this number called my client and said he was being investigated for a fraud case and the he needed to call this number back or the police would be there to arrest him in the next 45 mins. They also said they had mailed him several letters which he has chosen to ignore.