I think I must have missed a step somewhere. I changed the crontab to:
*/10 * * * * usr/bin/php /var/www/html/website/include/cli/modules/cron.php > /dev/null 2>&1
but still nothing is happening. I tried to run the cron.php file manually:
/usr/bin/php /var/www/html/website/include/cli/modules/cron.php
and I got: PHP Fatal error: Class 'Module' not found in /var/www/html/website/include/cli/modules/cron.php