Plagiarism is I guess I could say a pet peeve of mine I have had instances where people have used my photos without permission or crediting as a source which is so frustrating as a photographer in my case but equally so for writers and other creatives
Well written post on this subject
And it always leaves a bad taste in your mouth when you see your work stolen by others and no action taken on thieves even if you report them to competent authorities. I have had a couple of similar experiences when I found my article in others' names and admins didn't even reply.
So sorry to hear you have experiences that is is so frustrating and terrible the admins do not even respond to you that is atrocious