With the debt being discharged, they cannot try to collect the money from you. They can still exercise their rights as the lienholder and repossess the car.
There's not so much an "what they think they are owed", as there is "the amount that they're owed". Your debt is governed by your loan agreement. If you don't understand how they have reached the balance that they state that you owe, to have them relinquish their lien, ask them for an accounting / explanation.

