Can I claim a loss of money sent to my granddaughter, through the post office?

I wrote several handwritten letters to the Postmaster, and because I was never told that I could not send CASH and I did not make copies of the bills for my records, by the fourth letter from the post office, I was sent a check to cover the cost of the insurance and the mailing fee. The post office beleived the assistant post master in Winnie, TX, that the priority mail pouch had been returned to me and perhaps under a new priority number. I assured I had never received the priority pouch under any number.  I was out of luck and lost $600.00! Can I claim this loss from last Jaunary, 2023?