COD problems

[VWGTi@aol.com]

OK Guys Problem....

I had an amp i was selling over the internet.  Sold it to a guy in Washington
state.  Shipped it out COD.  Well today he called me saying he got the Amp and
he paid for it with a check (which i had requested cash or money order only!).
He then told me he had stopped payment on my check and that i wouldn't be able
to cash it.  

Now what do i do?  He has my amp.  He refuses to pay for it or even ship it
back to me and if i try to cash his check i won't be able to?  

Can i file a claim for it through UPS?  I am not going to drop it because its
a $250 COD order.

Any ideas?

Jeff