If they're insured, go (note: go in person) and 
get the post office to pay up for damaging them. 
If they tell you that you have to give up the 
cels, refuse. This is not a "you break it you buy 
it" situation. The cels are still yours. If they 
tell you they need them for evidence, tell them 
they can take a picture of the cels. That is all 
the evidence they need.

If they still won't pay, demand back the money 
that you paid to have the cels insured. that 
should throw them for a loop. ^_~

At least they weren't completely mangled!! o_0;;

Many Sharp Smiles,
--Drac