Get some Fairy Powerspray spray cleaner as advertised by Ainsley Harriet. It's not a cheap cleaner, but it cleans ovens and hobs like nothing I've come across before. It will certainly remove the plastic residue.
Wear gloves when using it as it contains Caustic Soda. This stuff cleans very dirty ceramic hobs and ovens to perfection. Follow the instructions carefully and make sure you don't leave it in contact with the surface for longer than 30 minutes as it states on the bottle.