My question involves child support in the State of: Pennsilvania

I was paying child supportsince 2006 to my girlfriendfor our children.
2 years ago we got married and she cancelled the child support case. I received a letter of the change my account was $0.00
Marriage did not last and now I filed for divorce indigently and granted, filed for alimony pende lite pendding. While trying toretrievemy account fromchild support website(Pacses) I found out I over paid 6,000.00 dollars.
I talk with the social worker in charge of the account and saw the error and try to give me a tecnical excuse. I argued and she told me, they did not have the money, all was transfered to my wifes direct account. She told me to sue her to get theoney back.

I call her and asked for the copyof record and I got them in the mail next morning.

What should I do know?
Send her a letter or go to a small court and filed a claim to recover the money...?

Please some help