called you and said you owed it, doesn't mean you actually did. Assuming you did owe it because you agreed to pay it, how are you getting screwed by paying the tax you owed originally? Plus, if they agreed to a payment plan they should have provided something in writing saying so. If you didn't get this, you are out of luck, but stating you got screwed is incorrect. Paying a tax you didn't owe would be getting screwed. Not paying a valid tax screws everyone else.