Disqus plugin not showen on my theme.

A years ago I decided to get rid of comment.php file on my theme (I code it myself)
Instead I use one line of code in single.php theme file :-

<?php
   ?comment_form(array('comment_notes_after' => ''));
 ?> ?

after I enabled Disqus , and I opened an article on my website, Disqus weren’t shown at all.
when I tried default them e.g. twenty-sixteen it immediately shows up on that page.