I have tried using Plugins to remove 72K comments with no success

Based on the information on your question, it’s hard to confirm where your issue is coming form. However, here’s one sure way of finding and deleting all of your comments from your website:

  1. Make sure you have a working database backup before proceeding.

  2. Go to your WordPress database via phpMyAdmin, you should see a list of all of your tables

  3. Check both the wp_comments and wp_commentmeta tables and select the Empty option:

Confirm the action and all of the comments will be removed from your database. You should not see any more comments (pending, trash, published, etc).

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