Do I have rights to joint bank account after divorce

Well, "it depends."  Presumably, the divorce decree made no mention of who owns what in this account and there is no agreement between you and your ex.  Also, presumably, all of the money in the account was actually earned by your ex after the divorce and so is his separate property.  So the money is his; on the other hand (and assuming you are correct) he owes you money under a court order.  So if you took what he owed you, he could very well complain that you took his money, but your response would be that he owed you that money anyway, so any suit would be neutralized by a counterclaim for the same amount.  But, long term, that is no way to go on with your lives.