Consumer Redressal

I bought a Sony Xperia Z2 from Croma, Aundh, Pune on September 10, 2014. Within a week the screen of the phone developed a long hairline crack from top to bottom while it was charging. I did not drop the phone.Nothing was dropped on the phone.There are no physical damages.I had asked the dealer if the warranty covers all damages. Dealer said yes but warranty does not cover physical damage. The water-proof phone got overheated and the glass did not find space to expand and cracked under the pressure of the panel. Why such a costly product supposed to be water proof and scratch proof develop crack all by itself in just two weeks? Phone is lying with SONY service center for 1 month. Phone costs 45k, Sony asking me 17990 INR for repair. Online citation of customers show that phone has a self cracking defect.In spite, of possibility that the product is defective,Croma and Sony, did not cooperate with me.Why are they allowed to sell substandard products at so high a price?