wp_get_attachment_url and custom post type, not refreshing?

Hello,

I’m actually trying to get the attachment url for a custom post type I use, for my homepage (http://www.soykje.com/testeur/).

My problem is that when I change the image of my CPT (an article), I can’t get it on front… Seems like the code doesn’t get the last version. Nevertheless, if I use the the_content function, there is no problem and I get the last version/image of my CPT.

Do I miss something? Maybe I don’t use correctly the wp_get_attachment_url function?

Thanks by advance for your help!

Here is my CPT declaration:

<?php

add_action( 'init', 'register_homeimg' );

function register_homeimg() {
	register_post_type('homeimg',
		array(
		'labels' => array(
			'name' => 'Image d\'accueil',
			'singular_name' => 'Image d\'accueil',
			'add_new' => 'Ajouter une image d\'accueil',
			'add_new_item' => 'Ajouter une nouvelle image d\'accueil',
			'edit_item' => 'Editer une image d\'accueil',
			'new_item' => 'Nouvelle image d\'accueil',
			'view_item' => 'Voir l\'image d\'accueil',
			'search_items' => 'Rechercher une image d\'accueil',
			'not_found' => 'Aucune image d\'accueil',
			'not_found_in_trash' => 'Aucune image d\'accueil dans la corbeille',
			'parent_item_colon' => '',
			'menu_name' => 'Image d\'accueil'
		),
		'public' => true,
		'show_ui' => true,
		'menu_icon' => 'dashicons-format-image',
		'capability_type' => 'post',
		'hierarchical' => false,
		'menu_position' => 6,
		'supports' => array('title','editor')
	));
}

?>

And here is my code, for my homepage:

<?php
/*
Template Name: Accueil
*/
?>

<?php get_header(); ?>

    <section id="content" class="home">
        <?php $mainimg = new WP_Query('post_type=homeimg'); ?>
        <?php while ($mainimg -> have_posts()) : $mainimg -> the_post(); ?>

		<?php
			$args = array(
				'post_type' => 'attachment',
				'post_mime_type' => 'image',
				'post_parent' => $post->ID,
				'post_status' => 'any',
				'orderby' => 'modified',
				'order' => 'DESC',
				'posts_per_page' => 1
			);

			$attachments = get_posts($args);
			if ($attachments) {
				foreach ($attachments as $attachment) { ?>

				<p style="background-image:url(<?php echo wp_get_attachment_url($attachment->ID); ?>)"></p>

		<?php
			}
			}
		?>

        <?php endwhile; ?>
    </section>

<?php get_footer(); ?>