I would be really pee'd off. How dare they use YOUR quilt for a furniture wrap. As far as cleaning it. IF ALL ELSE fails , what I would do is try to unstitch some of the stitches in the back or front if the back is not pieced.I would then slip something flat and hard like a piece of plastic under the moldy backing (so the bleach doesn't bleach out the colors on the top side) and put slightly diluted bleach on the spots with a dropper or Q-tip so you can control the amount. Let it sit and watch it, bleach usually makes mold disappear. Then use a clean white wash cloth, wet it and blot the bleach out. Let dry. Then maybe wash the whole quilt on a gentle cycle.Hope this helps