Issue adding sub category programmatically

i am trying to insert products from an array.
The product is successfully created and the values are inserted normally except the sub-category.
The issue here is that the subcategory is registered as top level (no parent) or it’s not registered at all.
Anyone have any idea on what i am missing here ?

Outside from function

        $parent_cat_a= term_exists($myproduct['12'], 'category');
        $parent_cat_a_id= $parent_term_a['term_id'];
        eisagwghproion($myproductssimple);

Inside function

 $product_to_create = array(
            'post_content' => '',
            'post_status' => "publish",
            'post_title' => $myproduct['6'], 
            'post_status' => 'publish',
            'post_date' => $myproduct['22'],
            'post_parent' => '',
            'post_type' => "product",
                    );
                $post_id= wp_insert_post($product_to_create, true);
                if (!$post_id) //
                {
                    return false;
                }            
                update_post_meta($post_id, '_price', $myproduct['17']);
                update_post_meta($post_id, '_regular_price', $myproduct['17']);
                update_post_meta($post_id, '_sku', $myproduct['2'] );
                wp_set_object_terms($post_id, 'simple', 'product_type');

                                  if(strlen($myproduct['13']) > 1){
                    $parent_cat_a = term_exists($myproduct['13'], 'product_cat');
                    if($parent_cat_a !== null) //εαν υπαρχει η υπο κατηγορια
                        {
                            wp_set_object_terms($post_id, $myproduct['13'] , 'product_cat');
                        }
                        else //εαν δεν υπάρχει η υπο κατηγορια
                        {
                            $parent_cat_a_id = $parent_cat_a['term_id'];  
                            wp_insert_term(
                                $myproduct['13'], // the term 
                                'product_cat', // the taxonomy
                                array(
                                'slug' => $myproduct['13'],
                                'parent'=> $parent_cat_a_id
                                )
                            );
                            wp_set_object_terms($post_id, $myproduct['13'] , 'product_cat');
                        }
                    }
                    else{wp_set_object_terms($post_id, $myproduct['12'] , 'product_cat');}