Getting a list of specific pages with thumbnails

Hello,

I would like to display a list of pages (not posts…) with thumbnails.
But I want to display only the pages from a specific category. As I didn’t find anything to select pages from a category, I used metadata instead.
I tried several things, several tips from several support boards, and I finally got a working code…. Well, at least, it worked when I was testing it on my homepage. But now that I copy/pasted it into my custom template, it doesn’t show anything…
If I copy my entire homepage and paste it into my custom template, I get my exact homepage, but still without the page list….

So, here is my current custom template:

<?php
/*
Template Name: Catégorie
*/

get_header();

global $more;
$more = 0;
?>

	<div id="content-blog" class="<?php echo esc_attr( implode( ' ', responsive_get_content_classes() ) ); ?>">

	<?php
    $product_pages_args = array(
        'meta_key' => 'Categorie',
        'meta_value' => 'lycéens',
        'depth' => -1,
        'hierarchical' => 0
    );

    $product_pages = get_pages( $product_pages_args );
	?>
	<ul>
    <?php
    foreach ( $product_pages as $product_page ) {
	echo '<a href="<?php echo get_page_link( $page->ID ); ?>">';
	echo get_the_post_thumbnail( $page->ID, 'medium' );
	echo '</a>';
    echo '<li><a href="' . get_permalink( $product_page->ID ) . '">' . $product_page->post_title  . '</a></li>';
    }
    ?>
</ul>
	Do you see me? 

<?php get_footer(); ?>

I get my header and my footer, and the “Do you see me?” that is there to be sure there is a content. But my list of pages won’t show. I feel kinda lost because that exact same code works really well on my homepage.

Is there any way to get a list of my pages sorted by category (or metakeys) with pictures? Or can someone explain me how to make this code work? I’m really new to wordpress, started using it a few weeks ago and I don’t know much about php… Also, I’m sorry for my English mistakes, this is not my usual language.

I can’t show you the website because it’s still on localhost.

I still hope someone can help me.

Thank you.