WordPress – How can I get the input data from custom fields in WooCommerce Checkout?

I already add checkbox to show/hide custom field in my WooCommerce Checkout page at functions.php and the code is working well but I can’t get input data from my customer. Where/How can I get it? I’ve try so many code and losting my time too much.

Here is my code. Please help 🙁

add_filter( 'woocommerce_checkout_fields' , 'rws_display_checkbox_and_new_checkout_field' ); 
function rws_display_checkbox_and_new_checkout_field( $fields ) {
$fields['billing']['have_vat_number'] = array(
    'type'      => 'checkbox',
    'label'     => __('ต้องการใบกำกับภาษี', 'woocommerce'),
    'class'     => array('form-row-wide'),
    'clear'     => true
);   
$fields['billing']['vat_name'] = array(
    'label'     => __('ชื่อ – สกุล / บริษัท', 'woocommerce'),
    'placeholder'   => _x(' ', 'placeholder', 'woocommerce'),
    'class'     => array('form-row-wide'),
    'clear'     => true
);
$fields['billing']['vat_number'] = array(
    'label'     => __('หมายเลขผู้เสียภาษี', 'woocommerce'),
    'placeholder'   => _x(' ', 'placeholder', 'woocommerce'),
    'class'     => array('form-row-wide'),
    'clear'     => true
);
$fields['billing']['vat_address'] = array(
    'type'      => 'textarea',
    'label'     => __('ที่อยู่', 'woocommerce'),
    'placeholder'   => _x(' ', 'placeholder', 'woocommerce'),
    'class'     => array('form-row-wide'),
    'clear'     => true
);
return $fields;
}
add_action( 'woocommerce_after_checkout_form', 'rws_conditionally_hide_show_new_field', 9999 );
function rws_conditionally_hide_show_new_field() {
  wc_enqueue_js( "
      jQuery('input#have_vat_number').change(function(){
         if (! this.checked) {
            jQuery('#vat_name_field').fadeOut();
            jQuery('#vat_name_field input').val('');
            jQuery('#vat_number_field').fadeOut();
            jQuery('#vat_number_field input').val(''); 
            jQuery('#vat_address_field').fadeOut();
            jQuery('#vat_address_field input').val(''); 
         } else {
            jQuery('#vat_name_field').fadeIn();
            jQuery('#vat_number_field').fadeIn();
            jQuery('#vat_address_field').fadeIn();
         } 
      }).change();
  ");  
    if ( isset( $_POST['billing']['have_vat_number'] ) ) {
        $have_vat_number = $_POST['billing']['have_vat_number'];
    }

    if ( isset( $_POST['billing']['vat_name'] ) ) {
        $vat_name = $_POST['billing']['vat_name'];
    }

    if ( isset( $_POST['billing']['vat_number'] ) ) {
        $vat_number = $_POST['billing']['vat_number'];
    }

    if ( isset( $_POST['billing']['vat_address'] ) ) {
        $vat_address = $_POST['billing']['vat_address'];
    }
}

I’ve try by add this code but still not working.

add_action('woocommerce_checkout_update_order_meta', 'rws_save_custom_checkout_field_data');

function rws_save_custom_checkout_field_data($order_id) {
    if ($_POST['billing']['have_vat_number']) {
        $have_vat_number = sanitize_text_field($_POST['billing']['have_vat_number']);
        update_post_meta($order_id, 'Have VAT Number', $have_vat_number);
    }

    if ($_POST['billing']['vat_name']) {
        $vat_name = sanitize_text_field($_POST['billing']['vat_name']);
        update_post_meta($order_id, 'VAT Name', $vat_name);
    }

    if ($_POST['billing']['vat_number']) {
        $vat_number = sanitize_text_field($_POST['billing']['vat_number']);
        update_post_meta($order_id, 'VAT Number', $vat_number);
    }

    if ($_POST['billing']['vat_address']) {
        $vat_address = sanitize_textarea_field($_POST['billing']['vat_address']);
        update_post_meta($order_id, 'VAT Address', $vat_address);
    }
}