IRS scam. Been around for awhile. Originates in India or Pakistan. Do not fall for it. IRS never cold calls you about a tax dispute. IRS only initiates contacts by US mail. They are trying to scare you into paying them something by Green dot money pak which are untraceable.
Invest in a call blocker and do not pick up on call numbers you do not recognize. Don't be afraid of these scammers. Don't talk to them, do not return their calls.
Axiom:
If anyone with an Indian accent cold calls you and 1. threatens you or 2. offers you something, you know it's a scam and hang up immediately and block the call.
Corollary
Never wire anyone money if you do not know them personally.
File a complaint with the FBI on their Internet Crime webpage http://www.ic3.gov/default.aspx
The IRS never contacts people by telephone. If/when needed you will get a letter, either regular mail or Certified mail. This is a scam. Do not answer them. do not call them back, do not hire an attorney, do not pay them money. File a complaint with the FCC consumer fraud division.