Woocommerce WC_Form_Handler not found

Question

I'm newly using classes in my Plugin. Before I've used classes, my Ajax add to cart function worked fine. Now I'm getting this error:

Uncaught Error: Class 'system\core\WC_Form_Handler' not found

("system\core" is the namespace of my file)

Before I am calling Wc_Form_Handler::add_to_cart_action(); I'm checking if this specific class exists. So if the class wouldn't exist, the class wouldn't be called later...)
I've also taken a look into get_declared_classes(); to make sure that my classes are called after the Wc_Form_Handler.

Does someone have any idea how I can deal with that problem?

namespace system\core;

class Woocommerce{
    public function __construct() {
        add_action( 'wp_footer', array( __CLASS__, 'ace_product_page_ajax_add_to_cart_js' ) );
        add_action( 'wc_ajax_ace_add_to_cart', array( __CLASS__, 'ace_ajax_add_to_cart_handler' ) );
        add_action( 'wc_ajax_nopriv_ace_add_to_cart', array( __CLASS__, 'ace_ajax_add_to_cart_handler' ) );
        add_action('init', array( __CLASS__, 'remove_add_cart_handler' ),10); 
    }

    * JS for AJAX Add to Cart handling
     */
    public static function ace_product_page_ajax_add_to_cart_js() {
        ?><script type="text/javascript" charset="UTF-8">
        jQuery(function($) {

        $('form.cart').on('submit', function(e) {
            e.preventDefault();
            var form = $(this);
            form.block({ message: null, overlayCSS: { background: '#fff', opacity: 0.6, "border-radius": "30px", } });

            var formData = new FormData(form[0]);
            formData.append('add-to-cart', form.find('[name=add-to-cart]').val() );

            // Ajax action.
            $.ajax({
            url: wc_add_to_cart_params.wc_ajax_url.toString().replace( '%%endpoint%%', 'ace_add_to_cart' ),
            data: formData,
            type: 'POST',
            processData: false,
            contentType: false,
            complete: function( response ) {
                response = response.responseJSON;

                if ( ! response ) {
                return;
                }

                if ( response.error && response.product_url ) {
                window.location = response.product_url;
                return;
                }
                // Redirect to cart option
                if ( wc_add_to_cart_params.cart_redirect_after_add === 'yes' ) {
                window.location = wc_add_to_cart_params.cart_url;
                return;
                }
                var $thisbutton = form.find('.single_add_to_cart_button'); //
    //            var $thisbutton = null; // uncomment this if you don't want the 'View cart' button

                // Trigger event so themes can refresh other areas.
                $( document.body ).trigger( 'added_to_cart', [ response.fragments, response.cart_hash, $thisbutton ] );

                // Remove existing notices
                $( '.woocommerce-error, .woocommerce-message, .woocommerce-info' ).remove();

                // Add new notices
                form.closest('.product').before(response.fragments.notices_html)

                form.unblock();
            }
            });
        });
        });
    </script><?php
    }

    /**
     * Add to cart handler.
     */
    public static function ace_ajax_add_to_cart_handler() {
        if (class_exists('WC_Form_Handler')){
            WC_Form_Handler::add_to_cart_action();
            WC_AJAX::get_refreshed_fragments();
        } 
    } 

    public static function remove_add_cart_handler() {
        remove_action( 'wp_loaded', array( 'WC_Form_Handler', 'add_to_cart_action' ), 20 );
        add_filter( 'wc_add_to_cart_message_html', '__return_false' );
    } 
}

(edit)
Because the class gets loaded I think that this isn't the problem but could my autoloader be the problem?

spl_autoload_register(function ($class_name) {
    $location = __DIR__ . DIRECTORY_SEPARATOR . str_replace('\\', DIRECTORY_SEPARATOR, $class_name) . '.php';
    if (file_exists($location)) {
        try {
            require_once $location;
            return;
        } catch (Exception $e) {
            throw new Exception($e->getMessage());
        }
    } 
}); 

Answer 1

Alright, I got it! You need to define the WC-Form_Handler class as global.

    public static function ace_ajax_add_to_cart_handler() {
    if (class_exists('WC_Form_Handler')){
        \WC_Form_Handler::add_to_cart_action();
        \WC_AJAX::get_refreshed_fragments();
    } 
}