How to check problem when read a table in plugin ?

my order is :
            $db = JFactory::getDbo();
            $query = $db->getQuery(true)
            ->select(array('cal_n_sem','cal_c_j'))
            ->from($db->quoteName('#__mytable_calendar'))
            ->where($db->quoteName('cal_d').' = "'.$date_com_d.'"');
            $db->setQuery($query);

            $date_calendar = $db->loadObject();

class plgHikashopMonsite extends JPlugin{
	function plgHikashopMonsite(&$subject, $config){
		parent::__construct($subject, $config);
	}

	function onAfterOrderUpdate(&$order,&$send_email) {
            
            $orderClass = hikashop_get('class.order');
            $order = $orderClass->loadFullOrder($order->order_id, true, false);
                
            $db = JFactory::getDbo();

            if($order->order_status === 'confirmed')
            {
                foreach($order->products as $product) {
                    
...

                    $n_sem = $this->CalculSemaines($order->history[0]->history_created,$nb_sem);                   

                    for($ind = 1; $ind < $nbre_indice; $ind++)//insert a row in Abonnes for each product
                    {
                        $object = (object)array(
...

                        );

                        $db->insertObject('#__monsite_abonnes', $object);
                    }
                }   
            }

            return true;
        }    

        /* calcul de la semaine de fin abonnement = semaine de départ + nbre de semaine */
        /*-----------------------------------------------------------------------------*/
        [b]public function CalculSemaines($fn_date_order,$fn_nb_sem) [/b]
	{
            // récupération de la date & heure limite maxi d'acceptation de la commande (paramétrée côté admin).
            $fl_param_n_jour = JComponentHelper::getParams('com_monsite) ->get('fl_Jour_limite_pari');
            $fl_param_heure = JComponentHelper::getParams('com_monsite') ->get('fl_heure_limite_pari');
            
            //recup date & heure de la commande
            $date_com_d = gmdate("Y-m-d", $fn_date_order);
            $date_com_h = gmdate("H:i:s", $fn_date_order);
            
            //recherche du numero du jour de la commande 
            $tabDate = explode('-', $date_com_d);
            $timestamp = mktime(0, 0, 0, $tabDate[1], $tabDate[2], $tabDate[0]);
            $n_jour_commande = date('w', $timestamp);
       
            //recherche de la semaine liée à la date de la commande dans la table Calendar.
[b]            $db = JFactory::getDbo();
            $query = $db->getQuery(true)
            ->select(array('cal_n_sem','cal_c_j'))
            ->from($db->quoteName('#__footlisted_calendar'))
            ->where($db->quoteName('cal_d').' = "'.$date_com_d.'"');
            $db->setQuery($query);

            $date_calendar = $db->loadObject();[/b][color=#bb4444] => seems that get nothing when coming from paypal, ok when in admin part.[/color]


...
            
        }

$n_sem = $this->CalculSemaines($order->history[0]->history_created,$nb_sem);