Geyser replacement warranty

My insurance did sent the plumbers to check my geyser after I have reported that it is heating up anymore. Those plumbers said they couldn't do anything because the geyser is still under warranty. The geyser I am talking about was fitted on the 17 January 2019 (fortunately it was covered under warranty from the manufacturer (Gap Geysers). I am disappointed with Gap Geysers services: - because they don't understand the importance of communication at all. - at they moment they are refusing to fix my geyser simply because they have replaced my old geyser in January 2019. - they are only telling me now that warranty reverts back to the original geyser, thus there is no further warranty with the replacement of a new geyser, only the remaining period of the original 5 year period (I occupied my house in October 2014). - I am only being told today that the geyser which was installed in January had 30 day period to report defects thereafter I am on my own. - to my surprise, one of their administrator said the geyser stopped working because of electrical issue....element or thermostat (which are no longer covered by warranty. It seems like he is not even sure of the problem.

Please help, how do I resolve this issue?