Second time I got a call like this, had heard of this scam. I did not call back, just went on the IRS website and reported the callback number on their Report Phishing form. Hope they get these scumbags!!
Voicemail left. I'm keeping it for a while along with the one from Donald Trump (both just for laughs). Blocked the number they called from along with this number which was to be their call-back number.