Subscriptions – Get Price Per Month (Time period) from Wp_QUERY

Hi just wondering if anyone could direct me…
I’m doing the following:

 foreach ( $product_categories as $product_category ) {

       echo '<h4><a href="' . get_term_link( $product_category ) . '">' . $product_category->name . '</a></h4>';

       $args = array(

           'posts_per_page' => -1,

           'tax_query' => array(

               'relation' => 'AND',

               array(
                   'taxonomy' => 'product_cat',
                   'field' => 'slug',
                   'terms' => $product_category->slug
               )
           ),
            'post_type' => 'product',
           'orderby' => 'title,'
       );

       $products = new WP_Query( $args );

       echo "<ul>";

       while ( $products->have_posts() ) {

           $products->the_post();
          $product_id = get_the_ID();
			$product = new WC_Product($product_id);

// Ensure visibility
if ( empty( $product ) || ! $product->is_visible() ) {
	return;
}

  if(class_exists('WC_Subscriptions_Product') && WC_Subscriptions_Product::is_subscription(get_the_ID())) {
      echo WC_Subscriptions_Product::get_price_string(get_the_ID());
    } 

this will return 0 / month

I was wondering if anyone knew what I might be setting up wrong.