ethics - When to give up seeking justice after you've been plagiarized?

I found that a Ph.D. student, recently graduated, plagiarized over a dozen passages from a book I based on my own Ph.D. dissertation of some years ago. Their dissertation is on the Internet, which is how I became aware of the plagiarism. I am in the US, I should say, while the student’s university is in another country (not a third-world country, as someone asked, and it is one with rules similar to those in the US about plagiarism).

In most instances the student cited me as a source at the end of sometimes long, closely paraphrased passages. I believe this still constitutes plagiarism in the form of "excessive paraphrasing."

As UNC-Chapel Hill notes, for example:

Even if you cite your source, paraphrasing can still be plagiarism if all you do is rearrange the author's words, delete a phrase or two, or insert a few synonyms and claim the passage as your own.

When I reported the student to their dissertation committee chairperson, nothing happened. The chairperson did not even report the matter as required to the administration.

Dissatisfied, I took the matter to the university's director of student ethics, who told me I had a strong case not only for plagiarism, but for unprofessional conduct. The director assigned a random professor to investigate, who to my surprise absolved the student of wrongdoing. The only reason given was lack of evidence of intent to deceive.

Again dissatisfied, I took the matter to the president of the university, who agreed to hear my concern. Once I revealed the nature of that concern, however, the president no longer responded to me. Even the president's assistant, whom the president had included in the discussion, no longer responded.

I have been careful not to come across as a loon (between the president and his assistant, for example, I sent a mere four emails, only two of which were follow-ups saying "I haven't heard from you: can you confirm receipt?") In short, I think I have responded as any rational person might in such a situation.

I should add I am an experienced scholar widely known in my field. (Granted, it's a narrow field.) But because I am no longer affiliated with a university, I have no one to represent me. (My publisher did contact the student formally and threaten legal action, but, again, only if the student should publish the plagiarized text.)

I was told by an attorney friend there is no point involving attorneys because there is no material loss on my part. If, however, the student publishes the dissertation as a book, then an attorney could be involved, even if the loss involved is negligible. (We aren't talking Harry Potter, after all, but obscure academic works.)

My question is: at what point should I give up seeking justice? (I would have been content with the student merely rewriting the paraphrased material – but discussions never reached the subject of remediation. That's all I really want to achieve, and I think having been caught and having to revise the text would have been punitive enough for the student.)