Blocks of flats are insured as a whole and not as individual flats. You are entitled to copies of the policy and schedule to confirm this. Send copies to your mortgage lender to show that the building is insured.
Leaseholders who have been paying a building insurance premium to their mortgage lenders, even for many years, can reclaim their money by demonstrating that the property was already insured for the relevant period.
Remember that the building insurance will not cover the contents of your flat. You will need to make your own arrangements for this.