Okay here are a few things that need to be done:

First, Anime Assault is back.  They probably don't
want to take the scan down because it shows that
they can get good cels, so even though it is sold,
they want to keep it up.  This is the only
explanation I can think of that they ignored your
requests to take it down when it is already sold, 
and why they are answering everyone's emails but 
yours.  You now own cel.  In my opinion you have
every right to ask them to take down the scan of
a cel you already own.

Second, send an email to the seller again and tell
him that if he does not take it down, you are 
going to write safe harbor at ebay and tell them
that he is claiming to be selling an original item
that you own.  I know it seems a pain for you to
do all this work when all you did was buy a cel, 
but you will be protecting people who don't read
this forum.  So it's worth it!!

Third, send an email to ebay anyway.  I have 
reported two people to safeharbor since I started
using ebay and both times they looked into the 
matter.  I was disappointed that all they did both
times was warn the other person not to do it 
again, but it's better than nothing.

Good luck with that!!!