My process was as follows (on a damaged frame from Belgium that had an insuranced value of $1,000usd):

Pictures as documentation of box and packing and frame damage.
Send pictures to the shipping company/person
Get them to file claim (w/ all your pics) with initial delivery service (mine was BE postal service)
The initial delivery service contacted the USPS (but could be any other company)
USPS sent me a letter (while I was out of town)
1 week later I went to the post office, I was informed that USPS had informed BE Postal that the damage had not been verified in person.

After 2+ months, Claim = Denied ; and I have to say, the shipping party was generally cooperative with paperwork and communication.

Maybe we should have used FedEx, UPS, DHL, etc. but I trusted an 'experienced' seller.
Sometimes international shipments of large packages are subject to mishandling.

Sorry to hear of your loss. Good Luck. Be patient.