Montgrey unhelpful

We have an insurance claim against the body corp of our complex, for a stove/hob that was installed before we even bought the place, they refuse to fix/ replace the unit and say it not against them, as it is a built-in unit, it is part of building insurance and not content. The agents refuse to resolve this, they also accepted an invalid COC, which would have indicated that there was an issue, if it was done properly