Tenant Liability for broken glass

Other

Tenants of a ground floor flat reported a break in to the police and to me. In the course of whatever went on 2 double glazed units were smashed and a door panel was kicked in. There is a clause in the AST that defines the tenants responsibility to maintain the glass of the property. There is also a clause in the AST that states that any action caused by or allowed to be caused by the tenant that increases my insurance premiums is liable to be back charged to them. I have a property maintenance agent who carried out the boarding up and thew subsequent repairs at a hugely discounted rate. The tenant refuses to pay for or take responsibility for the broken glass. They have not been asked to pay for any other damage on the property. Who is liable for the repair charges?

Regards