sony xperia crack screens

i have an Sony Xperia z1 one year old. the screen have an hairline crack. took is in to Vodacom. give me an quote of R 3300 to repair. all over the internet is problem about crack screens on Sony. the quote state only the labour cost and they is no cost on parts. why must i pay if Sony knows their is an problem on the screens? on the job receipt it state no damage on the cover, only screen crack