Unfortunately i do not know much about ClientExec and how the functions work. But I do know that if the script can be called in a web browser, that a cron can be setup to do the same thing which is to execute the script. If GET doesnt work you can use lynx or curl too, we will have to see how it goes....

But, you should check if that script only works if you are logged in, so try running it when you know you are logged out of CE.

If it doesnt work in your browser when you are logged out of client exec, then you need to run from the command line like my first example. If that one doesn't work

php /home/myusername/public_html/hosting/services.php 'rebiller'

you can try:

cd /home/myusername/public_html/hosting/; php services.php 'rebiller'

or

cd /home/myusername/public_html/hosting/; php services.php

Just make sure to change 'myusername' to the real username.

If you have a shell I would run these commands first and see what they do. If they work in shell, then the cron will work.