If the accident was not reported to the police, and no statements were taken from witnesses, it sounds like the insurance company are simply running it up the flagpole to see what the cat licks up. Try toughing it out - write back advising you are prepared to make reasonable reparation for damage, on production of a detailed account from the repairers, stating excatly the damage, cost of parts, labour and so on. I'm tipping they'll back down - if they do produce the details, and the cost is reasonable pay up and avoid further hassle.