Geyser Replacement

I asked Burgess to come out and look at my geyser that had a significant overflow on 15/12/2015. They inspected the geyser and said I needed to replace it. Given that the holiday season started the next day I wasn't about to argue so I said to them to go ahead. They did checked if the old geyser was still under warranty, which of co**** it just expired a few months earlier. They did a fine job replacing the geyser but now I have a problem claiming the monies back from my insurance. I have asked Burgess on more than one occasion to supply me with the serial number of the old geyser so I can submit my claim to no avail. All I can think is they replaced the geyser while it was still under warranty and don't want to give me the serial number, leaving me out of pocket R10k