I did have a call from this number and they left a message saying that they we're the IRS

Really?  On Christmas Day?  These people have no shame, let alone scruples.   If they call again, tell them you have a bridge in Brooklyn to sell them.

They left a message saying the IRS has filed a lawsuit against us

Yeh, right!  Scam has been going on for years.  Just keep changing numbers.

I was out of town for Xmas and came back to find a message on my land line that I was being sued and to call that number.  Which I just did and really cussed them out as they didn't tell me what it was for.  After my initial panic, I realized any real law suit is first proceeded by a demand letter and then being served with court papers and not by a phone message.  So I went online and checked the number and found this.  Thanks.  Now I am certain this was a scam.  By the way I also received a message from a 360 area code and a 202 area stating that I was being sued but no information.  This looks a big scam.  Also when I called the number back there was no identification to the company's name.