if you have time, call them up and waste their time. every person on the line uses up a channel for their calls, which i'm sure is being routed to some bumhick place in india. which will cost them a pretty penny in connection fees. i just wasted 5 mins of their time. when they ask for a phone number/address i give them the FBI headquarters information
keeps calling and harassing me saying I owe and I need to call them back when I call back I get someone who can barely speak English this is a scam and I am sick of getting this number calling me
I personally call them back until they stop answering my calls. I tell them that they are NOT the IRS and that they are a scam. I keep calling them back and telling them off until they no longer pick up the phone. Then I report the number to the IRS (https://www.irs.gov/uac/report-phishing). If everyone would call back and harass them back, their effort may cease to be worth the trouble!