Hello Amjid,
Sorry to hear of your dissatisfaction with Audi, but I guess you will be aware that Audi - as with all other volume manufactures- are simply assemblers of vehicles, using parts supplied by a variety of suppliers.
One question:- You mention taking the car for a wash. Do you do this, and if so do they use a jet wash?
As annoying as this is, I think it is very common to find surface rust on the brake discs ( the Americans call them rotors) on cars of your age or younger. Corrosion on the calipers? Depends on how the car (wheels) have been cleaned.
Appreciting that brake calipers get hot, you are probably aware that the process of powder coating involves oven treatment to cure the coating.
Judging by the number of cars I see with gaudy painted calipers ( tarty and boy racer in my book!, but I'm of a different generation) you could follow suit and tidy your up by this DIY process I guess. Probably less hassle than doing battle with Audi.
Kind regards,
Gareth.
p.s. My comments may be moderated when we see the photos.