You need some thinners it will melt it straight off the window without damaging the demister. Carby cleaner will do the same job too

Suprised you're having issues with wax and grease remover.

Try substantially wetting a cloth with it and dousing the affected areas, leaving it for about 10 seconds then wiping.

If you can get to it without damaging the demister bars try scraping with a razor blade.

I'll try soaking it, otherwise Ill get carby cleaner/sodium hydroxide (heavy duty degreaser recommended my might car mods) tomorrow.

Thanks for your help guys.

Done.

Isopropyl Alcohol.