They did leave a message stating they were calling from the IRS and that 1) a lawsuit was being filed against me; 2) I would be arrested in 45 minutes; 3) I would be put on a bus; 4) bank account would be frozen; 5) driver's license and passport would be "taken away", etc.  So I googled the IRS in area code (562) and came up with this link:  https://www.irs.gov/uac/contact-my-local-office-in-California
Ok, first off, the call came in from India (I assume) due to the very strong accent.  I don't believe our government has outsourced calls to another country!  I had a really hard time understanding him so I called back a 2nd time and got someone with an equally strong accent.  Had a really hard time understanding this guy too so I started having some fun with it.  "I can't hear you, can you repeat that?"  "I didn't understand what you said, can you repeat that?"  Did that several times and finally the guy started yelling into the phone.  I could tell he was getting very frustrated!  So after my smoke break and my fun was over I just hung up and blocked the call.  Would be interesting to hear what others have to say!  Have FUN with them!