I just had the same thing happen. Seemed legit at first and then there are people I work with that said if you owe the IRS money they will call and serve you by a county server before they take any legal action. They don't just give you a one time notice.
I just received the same call, when I called it back a "foreign" person answered by stating his name and badge number and that they were from the IRS. When I asked to speak to someone who can speak clearly, he put me on hold; came back on and said that he is the only one who can handle my case. When he proceeded to tell me that he had an affidavit and that I owe 700 in federal taxes from 2008 thru 2013 I politely told him that I was going to contact my accountant along with my lawyer......click he hung up on me :)