Modified Child Theme PHP files, but no change on site

As above really. I made a copy of the parent comments.php file, and placed it in my child theme folder. I then modified the following line of code:

ORIGINAL

<?php       else : // comments are closed ?>
                <p class="nocomments"><?php esc_html_e('Comments are closed.', 'udesign'); ?></p>
<?php       endif; ?>

MODIFIED

<?php       else : // comments are closed ?>
                <p style="display: none;"><?php esc_html_e('Comments are closed.', 'udesign'); ?></p>
<?php       endif; ?>

I then uploaded my child theme comments.php file to my child theme, but nothing changed.

So, I thought maybe it was something to do with comments.php. So I tried to do something similar with page.php. Created copy, removed the get_footer() function and uploaded to child theme. Again, no change, footer still loading fine…

The strange thing is, all my changes made in my child themes style.css file work fine, it only appears to be php files which are being ignored.

Any help would be greatly appreciated.