Sony :: Laptop Screen- Vaio

I have a Sony Vaio Laptop. Its warranty ended 7th December. Phoned them to get it picked up and now they have it so any work should be covered under warranty.

There is a particle under the screen. I took a picture of it and emailed it to Sony who diagnosed it as dead pixels. They said they would repair it for free under warranty.

Now that they have the laptop they say there is a particle under the screen. They sent me a picture of it and the photo looks identical to what I sent them earlier which they diagnosed dead pixels.

Now they are saying it was accidental damage by me and want to charge to replace the screen (same price as I paid for the laptop).

I think that this is ridiculous and that they should repair it under warranty. They will not accept these two arguments:
1. If I damaged it then I would have had to have opened the screen which there should be evidence of.
2. If the particle got in some other way through a gap then it is a manufacturing flaw because there should be no way of a particle getting in there.