You don’t need that line in wp-config.php as wp-cron is enabled by default.
If you install the Cron View plugin you are able to see when the different jobs are scheduled. You can then trigger wp-cron manually by going to this URL with your browser:
http://your-domain.com/wp-cron.php?doing_wp_cron
If after this the actions you expected where successfully performed. You really have a problem with your hosting provider. Maybe he has cURL/fsockopen disabled or the DNS is not properly configured so he can’t resolve an IP for your domain. In that case you would need to contact tech-support.