Retrieving all the categories and their posts from a taxonom

function widget( $args, $instance ) {
        // Widget output
        extract( $args );

        $title = ( ! empty( $instance['title'] ) ) ? $instance['title'] : null;
        $level = sanitize_text_field( $instance['level'] );

        /** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
        $title = apply_filters( 'widget_title', $title, $instance, $this->id_base );

        // Get all the taxonomies to which this object belongs
        $type = get_post_type();
        $customPostTaxonomies = get_object_taxonomies( $type );

        if(count($customPostTaxonomies))
        {
            echo $before_widget;

            if ( $title ) {
                echo $args['before_title'] . $title . $args['after_title'];
            }

            foreach($customPostTaxonomies as $tax)
            {
                // Get all the categories in the current taxonomy
                $args = array(
                    'taxonomy' => $tax,
                );

                $myPostTaxonomies = get_categories ( $args );

                foreach($myPostTaxonomies as $myPostTax) {
                    // Get all the posts in the current category
?>
                    <<?php echo $level; ?>><?php echo $myPostTax->name; ?></<?php echo $level; ?>>
<?php               $categoryArgs = array(
                                'orderby' => 'post_date',
                                'order' => 'DESC',
                                'post_type' => $type,
                                'category' => $myPostTax->slug // seems not to be working
                                );

                    $postsArray = get_posts( $categoryArgs );

                    if( count( $postsArray ) ) {
?>              <ul>
<?php
                        foreach($postsArray as $myPost) {
?>
                    <li><a href="<?php echo get_permalink( $myPost->post_title ); ?>"><?php echo $myPost->post_title; ?></a></li>
<?php                   } ?>
                </ul>
<?php               }
                }
            }

            echo $after_title;
        }

        echo $after_widget;
    }