Insurer failing to pay out - appeal

Other

Two things I would like from you are a) advice for the best way forth b) have you had difficulty with an insurance claim? c) Should I just go ahead and repair the damage myself and look to just complaining about their process.
I used the recommended insurnace broker by the RLA and got a fab deal for insuring my houses. However, Equity (the insure) have failed to pay out on a claim for where meter section of a ceiling has collasped.
In short they say it isn't due to an obvious insured peril.
http://www.rentguard.co.uk/download-documents/equity/policy-wording/landlord-insurance.pdf
* the onus is on me to prove that it was caused by one

However, I feel broker and insurer have been negligent in following up my claim.
My accident was on the 5/1 it wasn't until Feb that they sent around there agent to inspect it. He took no samples, didn't go up into the attic to inspect it and did not touch the ceiling to see if there had been water damage.
They claim the ceiling has collasped due to debonding however the ceiling was artexed over lath and plaster it had no sign of wear and tear, in short it looked new. I couldn't have anticipated such an event to occur.

They claim the ceiling and laths were dry this is after inspecting it a month from the initial report.So I must give them evidence that it was from an insured peril however this is 3 months after the event now.

Help.