too many spam comments for the batch?

WP says our blog currently has 151,520 Spam comments. I installed & activated this plugin. Empty Spam button appears there on /wp-admin/edit-comments.php & when I click it it goes to /wp-admin/edit-comments.php?page=pw-bcpd-process & after a couple seconds redirects back and says all comments were deleted, but then I go back to Spam section and it still shows the same gigantic number (3,031 pages with 50 spam comments per page)

Am I doing something wrong, or missing something?

https://wordpress.org/plugins/batch-comment-spam-deletion/