There are dozens of stories about men paying child support for children that aren't theirs. This is a common issue and cannot be solved simply. Contact an attorney.
The theory of child support is honorable. The application of GA law is nothing short of highway robbery. Having paid thousands of dollars per month and picking up my kids without shoes or shirts is proof of the ineffective nature of child support to actually provide for the needs of the children.
I hate that for you and I'm so glad that didn't happen to me.
Just the thought of that makes me bonkers.
On the off chance that no one has told you today, you're a helluva guy.