dokan category drop_down

Hi,
i;ve made this menu to make some changes i want
but it’s not working can you tell me what i’ve missed??
i want to make the parent category disabled and not available to choose

$taxonomy     = 'product_cat';
                                        $orderby      = 'id';
                                        $show_count   = 0;      // 1 for yes, 0 for no
                                        $pad_counts   = 0;      // 1 for yes, 0 for no
                                        $hierarchical = 1;      // 1 for yes, 0 for no  
                                        $title        = '';
                                        $empty        = 0;

                                        $args = array(

                                            'id'               => 'product_cat',
                                            'taxonomy'     => $taxonomy,
                                            'orderby'      => $orderby,
                                            'show_count'   => $show_count,
                                            'pad_counts'   => $pad_counts,
                                            'hierarchical' => $hierarchical,
                                            'title_li'     => $title,
                                            'hide_empty'   => $empty,
                                            'exclude'          => '',
                                            'hide_empty'       => 0,

                                        );
                                        $all_categories = get_categories($args);
                                        echo '<select name="cat" method="post">';
                                        foreach ($all_categories as $cat) {
                                            if ($cat->category_parent == 0) {
                                                $category_id = $cat->term_id;
                                                echo '<option disabled>' . $cat->name . '</option>';

                                                $args2 = array(

                                                    'id'               => 'product_cat',
                                                    'taxonomy'     => $taxonomy,
                                                    'child_of'     => 0,
                                                    'hide_empty'       => 0,
                                                    'parent'       => $category_id,
                                                    'orderby'      => $orderby,
                                                    'show_count'   => $show_count,
                                                    'pad_counts'   => $pad_counts,
                                                    'hierarchical' => $hierarchical,
                                                    'title_li'     => $title,
                                                    'hide_empty'   => $empty,
                                                    'exclude'          => '',

                                                );
                                                $sub_cats = get_categories($args2);
                                                if ($sub_cats) {
                                                    foreach ($sub_cats as $sub_category) {
                                                        echo  '<option value="'. $sub_category->term_id.'">' . $sub_category->name .'</option>';
                                                    }
                                                }
                                            }
                                        }
                                        echo '</select>';

                                    update_post_meta($product_id, 'category', $get_data['cat']);