Lots of similarities from my experience and what others have reported. VM was an automated womens voice saying immediate action was required to avoid jail time. I called the number back and spoke to a 26yr old boy from Pakistan named "Alex Watson". After I informed "Alex" that the IRS Treasury Impersonation Scam Division was aware of their harassing people, he unleashed an array of very sexual questions. If you choose to call these scam people back, just to ask em to stop wasting time calling, I encourage you to state what tried to make them understand. Which is 1. IRS doesn't contact people by phone ever, its all mail correspondence.
2. Both their name and case # they'll give you are both lies.
Block their numbers and don't let these con men stress you out.