These are illegal scumbags, trying to get you to send money on pre-pad visa cards, say you owe the IRS and if you do not pay you will be arrested. The IRS does not call or threaten over the phone, they would notify you by certified mail of a balance and or levy notice. Report these scammers to you local authorities.
I got a call and they would not identify themselves demanded money, I told them to send a letter if they were the IRS, they hung up on me. So I kept calling them back not saying anything, and the man on the other end told me to go F*** myself, I just laughed and he hung up. Kept calling them back over and over and have not ever received a phone call from them again.