Why my post’s thumbnail is not showing up?

I have created a post with featured image from the Add New Post section, and now I want to retrieve the post with it’s thumbnail , summary and the title.
The other fields are displayed just fine (title, and Summary) the way I want, however nothing can be retrieved for the thumbnail. Here is the code I’m using :

<?php
    $args = array( 'posts_per_page' => 1, 'order'=> 'DESC','category' => 'watch', 'orderby' => 'post_date','offset' => 1, );
            $postslist = get_posts( $args );
            foreach ($postslist as $post) :  setup_postdata($post); ?> 

            <td class="leftBoxes">
                <!--IMAGE- THIS IS the Problem -->
            <div class="imgMargin"> <?php  get_the_post_thumbnail(); ?> </div>

           <br>
            <div class="boxScrollsBlogsView">
            <h2><?php the_title(); ?> </h2>
            <P> 
            <?php the_excerpt(); ?> 
            </P>
            </div>

            </td>
            <?php endforeach; ?>

I added this line to the function.php as well

add_theme_support( 'post-thumbnails' );

and I can see the image when I click on single-post view, to check if it is added to the db or not.

But it just doesn’t come up in the custom page that I’ve created.