wp_schedule_single_event not working

You just need to hook your function to the hook you named in the second parameter of wp_schedule_single_event function.

See the following example:

add_action('woo_kala_order_note_added','woo_kala_order_note', 10, 2);
function woo_kala_order_note( $comment_id, $kala_order_id ){
    // do whatever your logic needs. 
}