My son is 18 and in college, he does not live with mother nor does she pay for any of college. I live in California, who takes care of the order?

Some states continue the child support up until the age of 21 for dependents attending college.
Below is a site with the relevant state information.
DADS AMERICA - Child Support over 18 (http://www.dadsamerica.org/cs18.htm)

If your support order states that support ends at 18 you need to contact the agency about ending the support.

You should have done this months ago. The agency can end it and they can help with it but they will contact the mom to confirm what you say and it could be delayed by months. The only faster way would be to file the papers for yourself.