A Father after 21 years

This is a long torrid story of deceit and lies that will likely make your jaw drop. I was married to a woman and we had two children at the time we divorced they were 2 and 3 years old. She quickly moved in with another man and he wanted to adopt the children. I was young and dumb and agreed to it just to get away from the mother and at the time thought it was the best thing for the children. The court had ordered that I pay $70 a month child support at the time of my divorce because I was still in college and unemployed at the time. When she decided she did not want me in the children's life any longer and wanted her boyfriend to adopt them, we signed a contract, notarized and created by an attorney that I relinquished rights forever for adoption of the children and that I was no longer responsible for child support. Now 21 years later I received paperwork that she had filed for payment of the child support. I have had no contact with her or the children, they are grown and serving in the military. She has hired a sleazy attorney that is on a 33% contingency if they win the case to get a third of what she gets. I have paid thousands fighting this, the attorney tells me that there is precedent to this case and that she cannot benefit after all of these years, when I actually gave up rights to the children 21 years ago. I assumed they were adopted and had long put this terrible incident behind me, but now it rears its ugly head. Can you believe that someone would be such a gold digger ? I am writing everyone I know, state and federal legislators, and will fight this all the way through the appeals court if it is not dismissed ahead of time.