No use warranty

I took out a contract with Vodacom in September 2015, sometime the first week in November when I tried to answered a call on my phone, the screen was acting funny. That's when I saw a small crack in the screen coming from the bottom between the middle and the right corner. It was strange because I have never dropped this phone, I was to in love with it to cause it any damage. I emailed Sony they said to return it to Vodacom, today Vodacom gave me a bill of R2700 to repair the screen that I didn't break. Which I'm not happy with, if I broke the screen I would gladly pay for it. No one can tell me how the screen cracked, they just expect me to pay for it and with this repair comes no warranty that the same thing won't happen to the new screen. Sony just says sorry the screen is not under warranty, which I read the warranty I still can't find it in there. I only see damage due to neglect and my phone was never neglected. So Sony won't replace the screen or even investigate it or give a guarantee on the new screen. The lady at support just says that is the rules she can't help. I will most certainly never buy another Sony product if this is the service they give.