Received a very threatening phone call saying i own substantial funds to the IRS.
They also said an arrest warrant had been issued.
The caller ID showed Unavailable but they left the number 202-864-1136.
When I called they identified themselves as an IRS office:
Mr. Calvin Jordin
Badge number 417306
An unnamed supervisor came on the line and gave me an additional number:
206-259-8844 x1211.
When you call both these numbers you get a voice mail saying you have reached the IRS.

When I contacted the IRS directly they confirmed that this was all fake.

There is a fairly common IRS or "tax scam" being practiced by scammers on both Canadian and USA residents.
USA tax payers should read this:
http://www.irs.gov/uac/Newsroom/IRS-Reiterate ... -Telephone-Scam

Short answer:
The IRS never initiates a contact via phone.
They always send a snailmail first.

Educational post:
This scam is also described as scam #11, here:
http://phonehelp.2truth.com/facts_rev.html

Remember to return here, to 800notes.com, after you look at any of the information at that site, either to post more information, or to let us know you avoided the scam, or to read any further information about that number that others may post.

Why these fake calls have not been stopped after so many years? Can't they be stopped? Why? The government can easily stop them using its power.

No, they can't be stopped.  They are hard-core Indian scammers and as such they are beyond the reach of US law.   The Indian government shuts them down once in a while, but they just spring up again.

Call blocker is your best bet.

Thank you for posting this online ！

I have just recived this scam call. same situation here.  On my home phone, the called ID appeared as U S GOVERNMENT. Saying that they have already filed up a law suit again me . wtf. I then called the provided phone number as 206 259 8844. a guy with accent asked my name, last 4 digit of my social ( too bad that I gave him) , but right before he ask me to provide my date of birth, I said " I'm not comfortable giving out these informations" . then I hung up.  
P.S. while I was on the phone, I can hear the background voice that his colleagues are  also taking calls.

For all the people out there, please don't give out your information.