the rep you spoke to was right they have no idea what you have. the reason is apple treats their like new replacements as new device. the back, button, battery and glass as all been replace and the device has been heavily tested to make sure it works
I understand how you feel when you pay your hard earned money for a brand new product, and it feels like the company doesn't care about what the consumer wants in return. It does feel like your getting a second rate product because the first product should've went through the rigorous testing. My Iphone 5 speaker sounds cracked like a tin can and they want to give me a replacement phone since they can't fix it. I'm thinking of looking outside of Apple to have a repair man look at it.
Apple wanted to give me a replacement for iPhone 4S for a cracked screen on a new phone. We got it replaced for $100 and it has worked great ever since.
I know Apple is a business and has to make money, but when brand new products are breaking down and the consumer feels like they're getting the bad end of the deal, it doesn't feel good.