First let me say I sorry to hear about your situation.
Secondly, I had sent Delta a letter regarding missing miles & they never responded to that as well. I therefore called the customer care department at 404-715-1450. I asked why didn't they respond to my request & agent made a phone call. It took about ten minutes but I got the miles immediately. I was told that my letter was read but was sitting on someone's desk waiting to be entered into the computer.
Maybe your letter is sitting on someone's desk as well. Call them and see.
Goodluck