[Ref: policy number]
Thank you for your letter of [date], offering only [£…] in respect of the [item], which was [details of loss/damage] on [date].
Since receiving your offer I have found a valuation certificate made by [valuer] dated [date] valuing the [item] at [£…].
In light of this valuation, a copy of which is enclosed, I feel your offer is too low and ask you to reconsider my claim.
I look forward to receiving your revised offer within 14 days.