I assume you own your flat, as if not, it's not your responsibility to claim property damage, just contents. Your landlord would be responsible for the repairs.
Secondly, you took out the Insurance knowing there was a £500 excess so I would just put it down to experience. If you decide to pursue through the Small claims court you must prove their liability, and unfortunately a lot of these situations do boil down to 'accidents' and are extremely hard to prove otherwise.