I'm under investigation by IRS and I need to immediately call his number.

This matches the other accounts. However this genius couldn't wait for the message recording beep so I only got the last half with the dire warnings and threats.
As stated above, The IRS will send you a letter if they perceive a problem with your return.
Today it does not pay to give your phone number to any business. They all must sell their lists.

Second call in two days and second message left about federal case. Not that they don't use other numbers but this does give me a number to block.

Same call - IRS investigation. My guy sounded Irish.

It is a scam.

The IRS does not initiate contact via a phone call, they first send postal letters.
The IRS does not threaten arrest.
The IRS does not demand immediate payment over the phone.
The IRS does not ask for Credit card, Debit card, or prepaid money card information, at all.

It is a scam ran by offshore criminals attempting to trick you into sending them money.
Hang up and report the call here:
https://www.treasury.gov/tigta/contact_report_scam.shtml
More info:
https://www.irs.gov/uac/report-phishing
https://www.irs.gov/uac/newsroom/phone-scams- ... 6-filing-season