IRS tax scam. The caller was claiming that my mother was named in a case involving the IRS. When I asked for the case number, he didn't have one and became angry and defensive. He was aggressively argumentative, with poorly constructed arguments, and a very poor grasp of English. His accent sounded Indian/[***]/Bangladeshi or from that region of the world.
We just received a call from these same people. We use caller ID and don't answer unknown numbers. Read Alfalfa's April 17 comments on here to get a clear picture of what is going on and what you can do. Tell anyone you know who might be gullible to never fall for these scams. The only way they will stop is if they no longer are successful.