I know this is an old post and it looks like the lid is fixed. If this happens to anybody in the future try this to get rid of the melted plastic , flip the lid upside down and fill it with ice. Let it sit for a while until both the lid and the plastic are cold. Then gently try to pry off the plastic You may need to sit the plastic in a bucket of ice as well. I have never removed plastic from a lid but had to remove burnt plastic from a piece of metal before and that how I did it .
Cheers