My ex claimed my daughter... What do I do?

My ex claimed my daughter. I have sole custody of her, she lived with me all year... Our court papers give me the right to claim her every year, and I never signed a release to allow him to claim her. I provided most of her support, in fact he was behind in child support most of last year. What can I do so that I can claim her? >:

[kumkum]

lawyer is best to advise on court matter