It sounds like the hub/driveshaft were removed from another model and fitted to your car, I'm not sure what model has 282 mm discs on the front but A3s and some Q3 models have rear disks that are 282 mm. I would agree that you check the local breakers for the correct hub, but check that your caliper matches the other side and driveshaft too. Either way having different brake disks and pads on any car is very dangerous and could cause major imbalance.