Wassem,
It's not not clear from your response whether you are actually running cron.php. That setting doesn't actually run cron. On one of your servers with Moodle code you need a line like this in the web server user's crontab:
*/1 * * * * /usr/bin/php /pathtomoodle/admin/cli/cron.php >/dev/null
You edit crontab on linux systems like this:
sudo crontab -e -u apache where -u specifies the user
https://docs.moodle.org/311/en/Cron
It's not not clear from your response whether you are actually running cron.php. That setting doesn't actually run cron. On one of your servers with Moodle code you need a line like this in the web server user's crontab:
*/1 * * * * /usr/bin/php /pathtomoodle/admin/cli/cron.php >/dev/null
You edit crontab on linux systems like this:
sudo crontab -e -u apache where -u specifies the user
https://docs.moodle.org/311/en/Cron