That money has been going to your ex. You need to make a motion to have the support suspended pending a hearing. If the support magistrate eventually rues that your support should have been terminated in September, you are going to have a difficult time getting those funds back from your ex. Under some circumstances, the court will not give you a retroactive credit for that support overpayment.
If the support magistrate hasn't suspended your payments or issued an order asked the SCU to hold your payments pending an outcome on your petition, then the mother is getting the payments. Once she gets the payments, if you prevail, she will owe you that money back. At that point, if she is working, you can ask that her wages be garnished until you ate reimbursed. Send a letter to the Support Magstrate asking that payments be suspended or make a motion to that effect.