woocommerce_order_status_completed not working

I think you must try changing $item[‘id’] to this

foreach ( $order->get_items() as $item )
{
$product = $item->get_data();
$item_id = $item->get_product_id();
 if( $item_id == 1136 )
  {
    // Keep Your code here. 
  }
}

Keep Posted.