Spontaneously cracked screen

I recently purchased a 2018 version MacBook Air. 3 months later, the screen cracks when I am typing on it. The screen started shaking, horizontal brown lines appeared then it went blank with crack lines appearing on the top left side of the screen. To the touch, I couldn't feel the lines. It seemed to be an internal crack. From the day I purchased the machine. I placed it on my work space and never moved it neither did it ever drop or get anything placed on it.

The machine is still under warranty but the repair shop has refused to do the repair. Please advice on a way forward...