Woah yeah it's way too soon to be getting hit with rust, just to double check, did you get brand new??I dont have much faith in trying the dealer and warranty to be honest... too many small prints and ways out for them.
Just very surprised that in this day and age a new car starts rusting so soon. I read that citroen only applies antirust on the outside of the body panels and not the inner parts... their reason is that it saves weight
I would not mind 1mpg less if it means my car doesnt rust!
On the bright side... as the car rusts away it should get lighter, and better mpg