you're kidding. it came out? Micron pigma pens are permanent. i always heat set mine too and have never had trouble. i've also used jelly roll pens. if you pen was different, i'd get another brand and write on the label again. you can do it even though it's sewn in. then heat set and hope for the best. but do a test piece first and wash that. should tell you if your label will last. sorry you've had trouble.
oops, just saw your pen was a micron. odd.very odd.
well make a label with embroidered info on it and stitch it over the old one by hand. that shoudl do it.