This is only my opionion not sure if it is the right answer but I would say that you both have moved out of NC then there is no reason for them to be overseeing your CS.
I would think that the x would have to file in her state where the child resides.
But just keep in mind that different states might not make it easier on you, they might say that you have been paying that much for this time and you can continue to pay that much, or worse they might make you pay more, and if your lucky very lucky they might lower it.
But until then make sure you continue the payments until the courts there order it so you dont get behind. That will look worse for you