...Next time try Super Clean degreaser...
Second that. I don't know how available it is outside of North America, but for anyone in the US or Canada, I recommend SuperClean. In my experience, it softens and dissolves paint within minutes. The longer the soak, the more paint will dissolve into the solution. Sometimes you can see the solvent work.
It can be used over and over, which is an advantage over other products, especially oven cleaners. I fill glass jars of different sizes to soak pieces.
I have also used it, applied with a paint-brush, to spot-strip paint to correct mistakes, without having to strip all the paint off.
I use it with metal, resin, and styrene. I have not seen any ill effects on any of those materials. It will weaken glue bonds, but that's an added benefit for me, since I usually strip paint from old figures I've purchased.
Also, as a de-greaser, it can be used around the home, too.
And at around eight bucks a gallon, that makes it a real bargain. I buy mine at WalMart, in the automotive supply section.
Prost!
Brad