They called, I didn't answer, they left recorded voicemail "against you. To get more information about this case file call please call immediately on our department number 650 479 3032..." I searched the number and people have reported it as a "you owe the IRS money" scam. Blocked the number.
I just got the same sketchy recorded message from this number. I called them back and a man with an Indian accent answered saying he was the IRS. There was so much background noise (sounded like he was at a street festival or loud mall food-court) that I could hardly hear him. He then wanted my information so he could identify my account... I told him that if he was the IRS he should have my information and actually know who was calling (I have just spent several weeks on the phone with the IRS getting a new business set up) and this was definitely NOT the IRS!
DO NOT GIVE THESE PEOPLE YOUR INFORMATION!!