I feel your pain. When I was 22 I bought my Type R, got a insurance quote with both parents on it. Was a good deal and then 2 weeks before it was due a woman rear ended my fathers M3. Cost £3.5k to sort but due to the value of the claim Bell (part of Admiral) put the insurance up by around £100. I was livid!
If the value of the claim had been £1k or under it wouldn't have effected it but neither do they take into consideration how much the car being repaired (at that time only 10 months old) cost and was worth.
According to them because he had been rear ended by some woman not paying attention he was now more likely to have a further accident. It's this statement I don't get. How? Plus why would he be more likely to have one and cause a premium increase because it cost £3.5k to sort but if it cost £1k he wouldn't be any more likely?
As mentioned, they make it up as thy go along!