Workmans Comp Audit on General Contractor

We were audited by our workmans comp carrier for a six month period. The previous audit we (A New Mexico General Building Contractor)were not required to pay workmans comp on a subcontractor who was a sole propriotor. The form we filed was a "New Mexico Workers' Compensation Administration Exemption for Construction Industry Licensees who are not Employers (Sole Proprietor or Partners). Our current audit the carrier said that we owe $8000 in workmans comp for sole propriotor licensed subcontractors that we hired. We replied that they were licensed sole propriotors with no employees. The response from the carrier was that the industry standards do not recognize this form and all licensed contractors were required now to carry their own workmans comp or we were liable to pay for the insurance. We explained that we were never notified of the change in policy and that we were conducting business as usual. Their response was that we still owe the 8K even if we were not notified.
Our Question is: Do we have any recourse through gov agencies or legal to protest the outstanding bill for past workmans comp owed. Thank you very much