It depends if you receive state assistance or not. If you did, some or all of the arrears go to the state, against the benefits they provided you. If not, the arrears go to his ex wife.
Please note that I am answering this question as a service through Avvo but not as your attorney and no attorney-client relationship is established by this posting. An attorney-client relationship can only be established through signing a Fee Agreement and paying the necessary advanced fees.
You might also try calling the child support payment clearinghouse, they may be able to give you a better answer on where the money is going.
This post is general information about divorce and family law in Arizona, and is not legal advice. Divorce is a complex process, and taking legal action without the one-on-one professional advice of a lawyer can produce unexpected results.
If the ex-wife received cash benefits (not food stamps or AHCCCS) for a child that she and your husband have in common, arrears first go to the state to pay back the money the state paid to your ex-wife. Once the debt to the state is satisfied and any associated fees paid, the remaining arrears payments go to the ex-wife.
You can reach DeWitt-Lopez Law, P.C. by calling 602.263.3900 or visiting www.dllawaz.com. All of my responses to questions posted on AVVO are intended as general information based upon the facts stated in the question, and are provided for educational purposes of the public, not any specific individual, and my response to the question above is not legal advice and it does not create an attorney-client relationship. I am licensed to practice in the State of Arizona. If you would like to obtain specific legal advice about this issue, you must contact an attorney who is licensed to practice law in your state.