take her back to court- it wont cost anything provided he represents himself as there is already an order in place., and keep a diary of what's going on- any contact made, texts or phonecalls received etc... if this keeps occuring then eventally she will receive a fine of £50 each time she refuses access, or a prison sentence. have you maybe considered letting him seeing his kids without you present?! ( just to save arguments and maybe create a happy medium?)