Please help . Not technically parenting related

I live in California. My boyfriend has a son from a previous relationship (let’s call him Z) and he is now 4 years old. As of last year we found out that he is on child support and money is being taken away from his checks weekly BUT Z lives with us! He is also the only biological parent with him because Z’s mother left them when he was 1 year old. So we’ve been going to court trying to get the child support off since he should not be paying if his son is with him and always has been. But on top of that . My boyfriends mother (Z’s grandma) is receiving benefits for Z like food stamps , medical, cash aid etc. Who can we report this to because not only is this fraud but my boyfriends mom won’t give us his insurance card so we can take Z to the dr and stuff. TIA