WordPress › Support » Thumbnails not showing

I've read about it in a couple of blogs but still didn't figure out why they are not appearing.

I can add a thumbnail image to each post on the back office, however they don't appear in the page.

I've noticed that in the content.php there is nothing calling for thumbnails although I've already tried to put this peace of code:

<?php
if ( has_post_thumbnail() ) { // check if the post has a Post Thumbnail assigned to it.
  the_post_thumbnail();
}
?>
<?php the_content(); ?>

and just to add,the following is stated in the functions.php:
add_theme_support( 'post-thumbnails' );

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