It sounds from your question like the mother is collecting child support though the state child support enforcement office. That office does not handle custody or visitation issues. Your husband will have to ask for that from the district court by petition. As for parentage, your husband signed on to that claim when he filled out the Acknowledgement of Paternity. Are you sure your husband is listed on the birth certificate as the father? Double check that fact. Even if it is too late to challenge parentage, he may have a fraud claim against the mother for past and future support. There are a lot of unanswered questions which he should discuss with an attorney in person.
If we do not have a written attorney-client agreement: I am not your lawyer; you are not my client; this is not legal advice.