Tablet quality and poor repair services

My daughter had the tablet and was playing on it as per usual. She looks quite well after all her electronics and it has not fallen since she's had it mid August as a birthday gift.

Whilst playing on it the screen cracked and here's the part that baffles me. The actual screen of the tablet cracked and would not work bit the tempered glass screen guard was not damaged at all. I then logged the tablet for a repair only to be advised they cannot guarantee the repair and I will be charged for the repair quote. This is clearly a product fault. Why should I be charged if I'm quoted an arm and a leg for a repair that occured due to normal usage?