Why is Apple not fixing THEIR error??

So, I have an apple macbook that I absolutely love. It's a great product, never had a problem with it-- till now. All of a sudden screen gets white w/ lines on it-- bring it into the store, they tell me its motherboard problem and it will be fixed under warranty, no problem. Next they send it in to get fixed and I'm told there is water damage & they want $800 to fix the LCD panel. Here's the problem--- I NEVER spilled anything, and no one else uses my computer. I have been relentless with Apple to try to get this fixed but nothing is happening. And, when my computer gets shipped back to me, the display looks completely different. It's now grey & splotchy.... interesting, yes?