Technically RS3's have a load index lower than OEM tires -- at least I think that's the sticking point. Discount Tires and other places won't sell or work on tires that deviate from OEM specs in certain metrics for liability reasons. I think Tire Rack now won't even sell you such tires if you indicate the car they're going on, so you have to buy them for an unspecified vehicle.
As was said above, bring them the wheels off the car or find another shop. And thank the excessively litigious people of this great nation and their obliging lawyers for your extra hassle. They're also likely the reason we can't close the windows with the fob or get Euro MDM by default.
