Maybe they are trying to recoup some costs from some repairs or storage?

I know of a mate who has a workshop was stuck with a car last year, he had done about £1800 worth of repairs and the owner was not able to pay. After a couple of months he sent a solicitors letter and sold the car, the excess was sent to the owner.

Probably worth a call to the auctioneers to find the out what is going on.

Steve