If you receive a call from someone claiming to be with the IRS claiming you made a mistake and owe money, it is likely a fake. I have received three such attempts and have a certain amount of entertainment messing with them.When they finally figure out that you're not going to give them a credit card number on the phone they roll out the abusive language.
Note that if you really do owe the IRS money, they will NEVER try to collect it with a credit card over the phone!