OP, you keep saying the FN2 is a 'double din'? Can you take a photo? I'm assuming this is a used vehicle, so maybe the previous owner replaced the factory head unit with an aftermarket double din. If it is, then I would request a good $500 from them and put it towards a head unit I would like. Think of it this way - They have dicked you around, but if you bought a car with a factory head unit, the fascia for the double din is already over $200. Then you'll have to buy a head unit. This way, half the work is done, and have the head unit is paid for. Anyway, if it's not an aftermarket unit, get them to pay you money anyway. A stock head unit is cheap on the forums and plenty of guys are trying to offload them since they have upgraded to a double din head unit.

Don't stress out, untie that knot in your panty and move on.