Hyundai breach of contract

We approached Hyundai ER to purchase a new H-1 Bus, on trade in of our previous vehicles, while we were being quoted on our old vehicles we expressed the fact that one of them is a code 3 - they quoted us and we accepted the deal - they had not viewed the code 3 vehicle and said it was not necessary. We faxed through the registration papers of both vehicles (which clearly states the code3) the morning before we took possession of our new bus. The next day we were told by Hyundai that they will not accept our old vehicle as it is code 3!! they want us to pay in the difference - after our contract has been signed! Now our permit has expired and they are refusing to give us a new one - All extras charged on the contract is now according to them not even in production.