I bought my fiancé paid by her pan for her birthday, and then set it still in the package on the back burner with the stove off. To remind us to season the pan. Of course I turn on the burner the next morning and melted the cardboard plastic covering stuff on the bottom of it. I tried scrubbing it and have one of those rings scrubbers and tried that as well. It doesn't come off in the slightest. Any advice?