legally separated from my wife I found out she has been receiving child support since 2012 we didn't separate til 2019 we were married living together

Your question is a little confusing.  It sounds to me like you say your wife has been receiving child support from you since 2012.  So I am assuming that in 2012, you and she were not married, but had a child together.  At some point thereafter, you got married, but no one notified the OAG or SDU.  An order for you to pay child support automatically terminates when the payor marries the payee.  Tex. Fam. Code 154.006(b).Since you say you need to file for divorce, I assume that you and she are still married, but have been separated since 2019.  If so, you need to file a motion to terminate withholding and attach a copy of your marriage certificate proving the date on which you were married.  It is a math question whether all of the support you paid through the OAG, including any tax refunds, exceeds the total amount of child support you owed from the date the order was entered through the date of your marriage.You might be able to argue that amounts you paid her other than through the OAG, via Zelle or PayPal, also ought to be credited to any past due child support you owe her for the time before your marriage.  The burden will be on you to show that those payments were specifically for child support, and not for another purpose.