This company is reading AND copying your material and using it in a commercial transaction with a third party.
Seems to me a simple matter to sue them for violation of copyright.
Bet these guys kind of wondered why NO ONE ELSE had done this!
>> “Every utterance you make on the internet is copyrighted and you own the copyright.” <<
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Not so on lots of sites, especially facebook. You have to accept their agreement, which gives them the right to use everything that you post to their site.
I would suggest posting on the interwebs is more like sending a letter to the editor.
If you don't want it to be public, you shouldn't publish it.
Email communication, in theory, is private, but a public post? Not so much.