If you don't want to go the lawyer route, you should be able to file a small claims suite against them for a nominal fee. My son did this for auto glass damage from a tree in a rental unit where his finacee was baby sitting. They tried all excuses not to pay but ended up settling just before the court date. Make sure you have lots of pictures and the installation contact if possible. If they were existing at the time of the policy they should be automatically covered and then the agency can go after the contractor. Good luck.
CB