Query a WordPress page by its title (which has a parent page)

You are almost there—but please, use WP_Query.

$args = array(
    'pagename' => 'features',
    'post_parent' => PARENT-PAGE-ID-HERE,
);
$query = new WP_Query($args);
if ($query->have_posts()) :
    $query->the_post();

    // ...

    wp_reset_postdata();
endif;

// EDIT:
If you don’t want to or cannot use the parent page’s ID, you can access it by its title, for instance like so:

    'post_parent' => ($parent = get_page_by_title('Designgo Silver')) ? $parent->ID : 0,