Strange child support situation

My ex relinquished his parental rights back in 2004, right before being sent off to prison. When he got out several years later, he started paying child support. He continued to do this right up until around 2014, when he discovered on the states (Oklahoma) online court dockets that our two children had their names changed. However, we have never seen a dime of the money. My now spouse and I decided at the time we didn't want the money of a convicted sex offender, and we just wanted to cut all those ties. However, years later, I realize it's my KIDS money, and not mine. My question is: Who could he have possibly been sending payments too, and after all this time, could my adult son and still minor daughter have some sort of claim on it?