Easy. You call the parents and tell them you will refuse him entry to your house. In fact, send an email too so you have a paper trail. Then call the school and let them know he is not to get on the bus to go to your house but his OWN house.
Then, IF the kid shows up anyway, call CAS. I would.
I would NOT allow a parent to strong arm me into caring for their kid. Seriously, you have to take care of it or he could just continue to send the kid for an eternity while not paying for it and every day you would just accept the kid without payment because you don't want the to feel "rejected"? That feeling of the kid is not on YOU - it's on his parents who were warned to NOT let the kid in your care without payment.

