Nedbank home insurance

We bought a house in December 2017 through Nedbank and we took the house insurance with Nedbank. In 2018 we experienced huge thunderstorms, whereby trees even caught fire - then we realize that the roof is leaking and the ceiling was damaged. On trying to claim from the insurance, Nedbank refused to take responsibility for the damaged roof, saying that the thunderstorm was not the cause of the leakage. Nedbank told us to fix the roof and then call them to replace the ceiling. How can you take responsibility for something which arose as a direct result of something that they claim they are not responsible for it does not make sense to me.