How can I get an accounting of my child support payments?

The Georgia Division of Child Support Services sent me a letter saying that because I’m behind on child support, they are going to intercept my federal tax refund. I dispute that I’m behind – I paid my ex in cash for 2 months worth of support. I was out of work and the child support office couldn’t get money from my paycheck so I just paid my kids’ dad directly. I told him about this letter and he keeps saying he’ll call the child support people and let them know I’m not behind, but he hasn’t done it and I’m getting ready to file my taxes. I can’t have that refund taken because then I will have double paid him for 2 months of support. How can I get an audit of my account and confirm that I don’t owe back support?