if not you need to talk with an attorney about you local laws. Many have clauses that state 6 months of nonpayment non presence as suitable grounds to file for restricting parental rights.
As for the taxes. While it might be a pain, when 2 people file the same kid, the IRS sends letters asking for documentation. If you provide them with the documentation that you are the custodial parent you will eventually get your refund if it is yours to claim. Is the tax exemption addressed in the decree? Even if dad is entitled to the exemption, you still get to count the kid for daycare and EIC.