robo-call message; IRS fake message

I received a message on my home answering machine that told me that the IRS was instituting a law suit against me and I was to call this number.  I checked with the IRS and this was not true.  I reported this to both the IRS and the Treasury Department.  When I called this number to tell them I had reported them and to not call me again, the man who answered identified himself as and IRS agent and when I told him I knew this was not true and that I had reported them to the IRS and Treasury Departments, he told me to wrap my open mouth around this big d**k.