This is just a scam where somebody cold-calls, pretends to be IRS and tries to scare you into paying money to somebody by Green dot money pak which is untraceable.
Ignore the call and do not return it. Block the number.
Report them: http://www.irs.gov/uac/Newsroom/IRS-Reiterate ... sive-Telephone-
Scam
Also here: http://www.treasury.gov/tigta/contact_report_scam.shtml