Repair of Xperia Z3 Screen - Under Warranty

Good day<br> <br> I've had my Xperia z3 for less than 6 months and last night when I was speaking to my friends on whatsapp I noticed that something felt weird on the back of my phone and when I turned it over the back had a hairline crack through right below \SONY"from the one side right through to the other side and I know for certain my phone did not fall or that I did not bump into anything as I was wearing pants without any pockets. It has fallen before when I got it the first time but no damage"