You should send him a certified letter informing him that he is in breach of the Separation Agreement (quote the paragraph). If you do not receive confirmation of the payment and the title to the car as agreed, you will be forced to hire an attorney to make a motion to the court to enforce this provision, and that he will have to hire an attorney to respond and pay for yours as well.
If he does not respond, you can proceed to enforce the Agreement in court. The court should allow you any immediate damages you suffered as a result of his breach.
Leonard Weiner, Esq. /Divorce Solutions