Child support and disabled adult?

My son will turn 21 next month and we live in the state of New York. My son has cerebral palsy and is under my care. His father has been paying child support for the past 10 years and has been sending notes on the final checks counting down until he turns 21, sounding obviously elated that he will not have to support his son any longer. Bear in mind that he does not spend time with his son (who has cerebral palsy) and the notes signal that after he turns 21 he will no longer have anything to do with his child and he is being very sensitive sending nasty notes to me and his son. Is there anything I can do as far as continued support since his son will not be emancipated at the age of 21.