You have done exactly what they want!!
If you tell them to sod off it saves them money, it is a business after all the more they can keep to themselves the better for them, don't play their games.
Phone up and speak to an underwriter, then go along and get estimates for the work what ever it is that's needed.
Write to them by all means but be polite, they hold the ACES wether you like it or not as they already have your money!!
Ask them what they propose to do about itm giving them "NOTICE"(14days) in which to respond.
were there any witnesses etc, what actually happened ?
tabetha