Oh No
Thats crap news matey, hope you get it sorted swiftly.
As for the diffusor, tbh I know you should not be left worse off but I would be tempted to just remove it and keep quiet, maybe mention to the bodyshop that you want it including in the price but not officially (they might be able to 'lose' the extra cost of it in the price of the whole job?
Not worth having to navigate the small print of someones insurance policy for something relatively minor.