I would have done exactly what you did: Offered to meet them halfway in rectifying the problem by trading down to what I had originally wanted and what I *was* entitled to for free. Then, when they refused, I would have politely but firmly told them to take my trade-in offer or leave it; either way, I would not be paying the extra fee which I had not only never agreed to, but which I had never even been told about.
Good for you for standing up for truth and justice!
Joy,
Lynn
