After a divorce, both parents are obligated and are legally bound to keep their side of the divorce decree. Although sometimes the arrangement is not adhered to, and a father may have to seek out legal mediation. An ex-wife who is not allowing court-ordered visitation, may be violating a court order, and the court might have to intervene.
If you ex-wife is not living up their end of the divorce decree, one might want to contact a legal professional for advice. One option that a legal professional may recommend is asking the court for a motion of contempt.
Basically, a person is guilty of contempt for not doing what the court has ordered them to do. Contempt is very specific to an individual case, so it is imperative that a legal professional be consulted before attempting to file contempt charges against your ex-wife.
The court has the ability to levy fines, award visitation as compensation or even amend custody agreements in cases of contempt. Speak to a legal professional to see whether or not you have a case.