Hey brother I'm sorry apple would treat you like that, its a sad story but happens regularly
I have see this before and it is not an easy fix to be honest, the connection to the back of the LCD sounds like it is loose
Let me ask, when you open and close the lid do the lines change or disappear, and if you tap the back of the screen will the lines change or disappear? If so that is what is going on, if not it might actually be the LCD going bad but my money is on the connection to the back
What you would have to do since it is an air is take the bezel off which is glued to the screen and then just remove the LCD screws and u can get to the back of it and test the connection, hopefully you can re-seat the connection and it will get rid of the lines
This will test if the LCD is bad or the connection, if you determine that the LCD is bad then you will have it already apart and ready to replace the LCD, I found a few on eBay, used for around 100$ and up, New 200$ and up, if you didnt feel like messing with all the taking apart of the screen you can find whole screen assemblies for around 300$ and up, good luck and hopefully apple with start doing better for their customers...doubt it though...