Had 2 Robo calls stating "IntIernal Revenue Services:  The reason of this call is IRS is filing a law suit against you.  For more information about this case file, call immediately on our department phone number  423-920-4284."

I received this message yesterday as well.  When I dialed the call back number, I received a message saying something to the effect of "the number you have dialed is not a working number."