I once had the very same problem with my dark red Bella:
I totally ripped it off at the back when the seem got caught by the heels of my shoes. No way to fix it. Sent it to Bella and they exchanged the chiffon with the best matching color they could find. The chiffon was a bit different (little bit lighter, different quality) but it was totally o.k. to me. Payed 50€ + shipping.
On Bella costumes in that style usually the chiffon is sewn to the top by hand after the top was beaded, so the chiffonpart is very easy to replace.