I'm really sorry that this happened to you.  
But relax; don't give yourself a heart attack over 
a damaged cel.  I have had a lot worse happen, but 
I understand that nothing is worse than when it 
happens to you (and believe me I felt that way when 
it did happen to me).
My reccommendation is that you ask the seller to 
mail you a filled-out insurance claim form, plus 
the insurance stub and that you go file a claim at 
the post office to get your money back.  Most post 
offices will make you surrender the cel, but 
sometimes if you word your request correctly, you 
can get away with just handing over the empty 
mailer (a bit of slight of hand will also work).

Good luck