There's a law working it's way through the Missouri legislature that will permit dads to challenge final paternity judgments under certain circumstances.
What has been happening is that men would be named as the biological father of a child who is not really their biological child in an administrative action. The man then either throws the paperwork from the child support agency away because he's sure he's not the dad (you laugh, but it does happen) or blows off the hearing. Since the man doesn't seem to object, the child support agency makes a finding of paternity against him and enters a child support order.
As it usually happens, time goes by. The man (who is now declared to be dad) forgets all about the paperwork he got from the child support folks. Then, eventually there comes a knock at his door. The next thing that comes about is a warrant for his arrest for nonsupport or his paycheck is garnished. Neither of these results is exactly good news for him. After all, remember, he's not really the biological dad of a child - at least not as far as he knows.
So - a bad result has happened.
The first thing that springs to the guy's mind is: Wait a minute - I'm not this child's father. So off he goes to hire an attorney to fix it.
Under the current law, the child support part of the problem doesn't go away. You have already had a chance to show you're not dad. You blew it off. So you can't complain now.
That's going to change in a significant way if this new bill is signed by the governor. If the bill passes, guys who have already been determined to be the father of a child will have a two year period to bring the issue back in front of the court, get paternity testing and get your child support arrearages (if any) taken off.
If the bill is signed into law, guys who are just now entering in the child support system, will have two years from the date on which the child support order is entered against them.
There are some other legal hoops that you will need to deal with if you want to bring child support up again. The only effective way to address it is to get help from your attorney. He or she will be able to guide you through the requirements.