Sony Z3 Experia warped

My husband bought a Sony Z3 Experia about November 2014. Recently, we took the phone off charge and found that it had warped (bent) on one side. We sent it in for repairs and the technicians report came back that the phone was damaged and too expensive to repair. The report showed the back screen was cracked, paint peeling, all untrue, apart from some scratches, the phone is in perfect order. I spoke to a Sony representative at the call centre who, although not having seen the phone himself, categorically stated that the problem was due to the fact that the phone was left on charge too long and thus it was a customer error, Sony would not be held responsible. He insisted that the battery had overheated and thus damaged the phone. I found this illogical as the phone is working perfectly, no swelling of the battery or other indication of damage. My main concern was that there was clearly a fault with this phone as it warped while charging and as it was a fairly new phone, it would probably not last the contract period. I am very disappointed at the lack of responsibility of the Sony representative and fear I have a phone which is potentially hazardous and a danger.