My friend who had not answered my letters wrote me about very prosaic reasons his silence. In the local post office worked the mailman who “liked” mail from the USA. He was probably looking for money in these letters. Next, independently of the result, he was throwing away mails to the garbage.
This guy doesn’t work in this post office any more. Right now, I can send letters to my friend because “obstacle” has removed. I got back my friend who I have never lost.