Just to square the circle:

Tried to call 'damage department' last Friday, no response on 4 x calls (going through to German answerphone message) so sent email to UK customer service asking for assistance.

Called 'damage department' again yesterday, picked up on one ring, agent checked record and told me that the entire sum for damage had been refunded due to their not receiving a proper reply from the station.

So it took a while but ^ to Avis.