Edit: as others have noted, the HTTP referer is not really useful most of the time - if at all (though legitimate, known good referrers may exist).
So what's left is 1) filing a DMCA request with their registrar and 2) hosting provider, 3) checking offending inbound links and using Google’s Disavow Links tool. And if they're plagiarizing some contents, also 4) asking Google to remove infringing pages from their index. I had to do the latter a few years ago.
So what's left is 1) filing a DMCA request with their registrar and 2) hosting provider, 3) checking offending inbound links and using Google’s Disavow Links tool. And if they're plagiarizing some contents, also 4) asking Google to remove infringing pages from their index. I had to do the latter a few years ago.