Refusing to pay for phone to be fixed.

Im from Durban and sent my phone to ssscellular In Boksburg to get repaired under warrenty. As i have never dropped my phone it started to crack under the screen guard which i was told when i bought the screen guard that, That would crack first if dropped. NEVER DROPPED MY PHONE but yet there is a crack. On the side of the phone where the crack has started there are no marks showing the phone dropped but yet get an email saying physical abuse on phone and warrenty wont pay. The one thing i will say about Sony is that when the screen is slighly cracked u cant use the phone but on a Samsung you can so right away thats me done with sony. I will not pay R3378,00 for my screen to be fixed as that almost a quarter of what the phone is worth. I have had a HTC for 4 years dropped it now and then but screen never cracked. Sony is useless.