Just received the same called with very unclear name (feel it is on purpose- teh guy has both accent and blurting words).
Presenting himself as IRS officer -investigating my case.
Guy tried this on me and I laughed as soon as he said "IRS". That pissed him off so I kept taunting him and insulting him (very cathartic). He finally gave up after 5 minutes of vain threats. He had what sounded like a Boston accent.