The freeze method should have worked bechasue it doesn't require you to pull. it seems like you were trying to spray the freeze spray under the mylar. This is incorrect. You want to blast the topside of the mylar with plenty of freeze spray... maybe 10 seconds if neccesary. The glue will simply let go of the mylar and the plastic lifts up easily.... almost by istelf. It just leaves the glue behind.

With the heat method, you likely had to pull; and now you have paint lifting.

Naptha, goo gone or even alcohol & flour method are your only options for removing the adhesive. With raised paint this will be sacry and I am sure that touch-up will be neceesary.

Post a picture and lets see how bad it is. Maybe it can be easily salvaged.

That would be a very easy touch up.

Once you get the glue off, I would see if there is any more of that art wanting to lift off the insert. If so, inject a little bit of "thin CA glue" underneath. It will find its way into every crevice.

Once that has set, you should be able to paint that area and either use Mylar or mask off the area around and do a spot clearcoat from a can and buff it out.

Good luck