Well known scam. Please take the time to read some of the posts on the main page & in the forum. Lots of information about many ongoing scams. You might find something to prepare you for the next scam.
I received two messages from this number yesterday. It seemed that it had to be a scam but it's still distressing when you first hear such a thing! Thank you for your information about what to do about it. I will report it to the Treasury Dept at the link you provided.
"Hello, we have been trying to reach you. This call is officially the final notice from IRS, Internal Revenue Services. The reason of this call is to inform you that IRS is filing lawsuit agaisnt you. To get more information about this case file, please call immediatly on our department number, 202-821-4201. I repeat, 202-821-4201. Thank you."