If you'd been paid out and kept the courtesy car you will be liable for the costs.

But thats your legal teams fault/insurance companies fault for bad advice.

When I had my not fault crash I got a car a few days later.. my solicitor who I must say was awesome advised I get the car picked up within a few days of recieving the payment for my written off car as I had funds to replace it.

Once I had funds to buy the car there it was not "fair" (uk law is based on equity and fairness) to have the courtesy car and the other insurers to be footing the bill.

If you had money to replace the car as soon as you had the accident I think that is irrelevant as the money was not ear marked for a car at the time as you had a perfectly servicable one.

Jake