I don’t understand why I would still owe money, if I have had handed the vehicle back?

Barney says:

When you signed up to the finance agreement with us, you agreed to pay us a certain amount over time to eventually become the legal owner of the vehicle. If you end the agreement early, you will need to return the vehicle to us and it’s possible you’ll owe us an amount to clear the agreement. Returning the vehicle to us in a good condition and in good time can reduce the amount you will owe to clear the agreement. If you’ve already paid us half of the agreement cost and you use the voluntary termination option there may be little or nothing to pay, other than any arrears or charges that are applicable.