Get all commenters on a post

I know there are several similar questions, but I couldn’t find the one I wanted.
I want to get all commenters’s on a post. But if there is a commenter who gives more than one comment, then he is not counted double. I don’t want to display them individually like:

Help with comments.php

I have a page with a shortcode that displays information from the database. I have set it up to allow comments on the page. The problem I am having is when I click Submit Comment, I get the following message:

How can I fix wp_insert_comment failure when ‘comment_content” includes slanted apostrophe in Excel csv source data

For the purpose of transferring a very large number of user responses from non-WordPress to WordPress comments, I’ve been given a Google Sheet. Regardless of the method by which I turn the Sheet into a CSV file (direct download as CSV, download as xlsx then save as csv, copy-paste into Excel and save), I get some version of the same problem, though with marginally varying results.