[GNC] How to Kill a Runaway Invoice?

[Jediator]

I was trying to reuse/repurpose an invoice ID for a customer (e.g. 
change the amount and date), but made a mistake of changing the customer 
name in between (not sure if was the cause).  Now I ended up with two 
invoices with the same ID on the customer report, with the old entry 
labeled as a Refund (with the amount still listed under Debits to AR) .  
I tried multiple ways to kill that refund invoice, but couldn't 
succeed.  Looks like the Invoice ID in GC isn't unique, so I ended up 
with two invoices and the old one just no where to find and noway to 
unpost.  Any suggestions how to kill that invoice (i.e., remove the 
corresponding entry in Accounts Receivable)?
Thanks a lot! -- JC