Lumia 650 touch screen common fault?

severstar

My 18 year old son has a Microsoft Lumia 650 phone on pay monthly in my name. He's had it 3 months, it's got a Gorilla glass screen protector on it and and a rubber case. He woke up to the screen only half illuminated on Saturday 28.01.17 then the display completely failed by end of the day.

O2 have determined there's a crack on "one of the layers of the touch screen" and that's causing the fault with the display. Yet, the protector screen is fully intact, the phone has never been dropped, rubber case has always been on whilst in use and there's zero damage/marks to the actual sides/back of the phone. The crack can be seen when you hold the phone under a specific light but it's impossible to photograph. It appears to be an internal crack, not on the outer touch screen

O2 maintain it's consumer damage not a manufacturer fault and therefore my problem. I'm not satisfied with this response (especially as I've now read reports of random internal screen cracking with the Lumia 650). My stance is, for an internal screen to develop a crack when the handset had only ever been used as a handset should be AND the handset has had an additional protrector screen since purchase then this particular handset is not fit for purpose.

Any advice or am I wasting my time taking it further? TIA