I actually had the same thing happen, and got all the plastic off by rubbing it with wet sandpaper...it took a while, but it did come off...
This works for plastic on a toaster, and it may work for you.
Acetone, specifically nail polish remover containing acetone. Be sure to read the label, since not all nail polish remover contains acetone. I learned this from Haley's book.
Unfortunately, it may have to burn off. All that would involve is a good exhaust fan and some open windows, and a nice day! However, plain ammonia is an excellent odor absorber. Place a small glass bowl or jar of ammonia in the unheated oven and let it there overnight. This may help, too.
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