I Wouldn't concede anything at this point.

A few years back we had the IRS claim we owed them some money. My wife made it through several lower level extortion agents, eventually a supervisor and went line by line down the tax form finally reaching the conclusion that their claim that we owed money was incorrect.

I obviously don't know your situation, but understand you are dealing with a greater level of incompetent bureau-rats than one can even imagine.