Is your property underinsured? If so it will be subject to average clause.
The term 'subject to average' means that if the sum insured at the time of a loss is less than the insurable value of the insured property, the amount claimed under the policy will be reduced in proportion to the under-insurance. Also called average clause.
If a policy of insurance covering a building has a sum insured of £80,000 and at the time of a loss the real insurance value is £100,000 then the proportion of Average would be £80,000/£100,000 or 80%. You will only receive 80% of any loss you suffer.
If you think you may be underinsured seek advice asap.