child support arrearage

My husband and I live in Ohio. Both of his children are now 18 so his monthly obligation is gone. He still owes arrears in the amount of 32,000. These arrears are his fault to being incarcerated and they piled up. His ex when they split up refused to let him see either one of the children which was completely wrong. He hasn't seen his children in almost 10 years. Now that they are 18 they won't even talk to him. He tried contacting them on social media after their mother blocked his number off their phones but she found out and blocked him off their social media sites. He now as I said is in debt 32,000 in cs arrearage. He was paying 800.00 dollars a month for 1 child including arrears till I helped him do a modification to get it dropped down to 460.00 a month. Now they are telling him that he will continue to pay that amount till its paid off. The prosecutor said in court he will have to pay what his monthly obligation was, which was 320.00 a month. My question is who is right? We are struggling as it is. Don't get me wrong. He should pay the arrearages because he owes that but what amount are they going to make him pay now?