According to information from the Wisconsin CNA Registry, if you worked under the supervision of a RN or LPN in the 24 months before your registration expired (which you said you did) then you might be able to renew your lapsed certification. You must submit a completed renewal form, signed by your employer, to report your employment history.
When the renewal form is processed, the nurse aide registry will be updated to reflect your eligibility to work in federally certified facilities. You can contact the Wisconsin Nurse Aide Registry at 877-329-8760 to verify this information. A representative will let you know if you can renew your certification or if you need to retake the CNA exam in order to reactivate your status on the registry.