usually best to get a council rep to meet you at site and show him , dont take no for an answer, i had a problem yrs ago and it was on a bridge over a motorway, which meant that i had to deal with the highways agency(shiteheads) and they eventually paid out.....the insurers for them were/and Zurich municipal!
or spk to your insurance comp as they do provide you with legal assistance!
good luck !~!~~