Your child support order should say until 19 or 18 and has graduated high-school, whichever should occur 1st. I am puzzled by the reference to DCSE not enforcing. The custodial parent may have closed their case with DCSE. The Division of Child Support Enforcement is optional, so it does not surprise me that the parent might have close their case.
I think you real issue is on the evidence. You feel that the other parent is failing to disclose income. You have the right to issue to discovery but you need an attorney to assist you. You may want to considered issuing an subpoena for his pay information directly to his employers.
You definitely need to sit down with an attorney to assist you.