I also received the same message saying the same thing. I called back they said they were from IRS filing lawsuit on me for back taxes. I ask what year. They said 2008-2013. Which I replied I paid 2008 they said I paid only the minimum. Now owe fees. I told them I had my letter and confirmation number which they wouldn't accept. I goggled this number and found this. So here is the hotline number for everyone to report this to 1 800 366 4484.
Caller: So called IRS