I've already had the same problem with an O2Switch server. Here's how to solve your problem.

In your crontab, you need to specify the full path of PHP as well as the absolute path of your project.

* * * * * /usr/local/bin/php /home/NAME/link_to_project/artisan schedule:run >> /dev/null 2>&1

This will allow the cron job to run normally.