How to make / escalate a complaint

I recently bought a iPad for my 9 year old son and it has bent in the middle on one side only. It has always been in a case and has never been dropped and has been well looked after.

I spoke with the support team via a call, sent them pictures and they recommended I take it to the local apple store either for a replacement if in stock or via mail service.

I went out of my way to travel to the store where I was told that a bend was "Normal" and that it was my sons fault and they would not replace it (Its only 5 months old). The Genius manager was very dismissive and quite rude. How do I escalate this complaint