Who is she living with? If the mom is on state aid, report her to the welfare office. If she's getting benefits for the child she may get them cut off or have to prove the child is living with her. If there is a support order against you you can file a motion to get it stopped. Investigating fraud isn't what child support does. They're basically a collection agency for the courts.
It depends if it's a serious matter. You should try calling department of families. Or an local child support number. You can also go directly online and look up your case.
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