How do I find out who claimed her and what can I do to fix it if it wasn't her father who claimed her if her father didn't?

Her father was court ordered per child support to claim her. I haven't received any payments from the taxes he was supposed to file. He has been dodging his payments and not reporting income properly. I want to request a change in the order which allows me to file her as a dependent for my own taxes since he is over 20,000 in arrears.