5 year warranty a ******* and treating customers as potential *********

I bought a geyser on 6/10/2018, the geyser came with a 5 year warranty. The sales man told me that if there is something wrong with the geyser I should come with the slip and they would dispatch someone to come and check. this past Sunday 2 Feb 2020 I went to the store and it was closed so Monday I send my brother with the slip to the shop as the water was cold. The assistant insisted that my brother get the serial number of the geyser which he could not see because the plastic film had fallen off. Tuesday morning we went back to the shop to at least log a call about the geyser, the shop assistant told us even before sending the email that kwikot will not help us without the serial number. We insisted that he log the call we took the number to try and call kwikot and explain. Before making the call a Lady from kwikot gave me a call and asked me what was wrong with the geyser I continued to explain and then the lady said kwikot cannot accept the receipt I got from the shop when purchasing the geyser, she would need a tax invoice from the plumber who installed the geyser when I bought it in 2018, I asked the lady why she needs the plumbers tax invoice and she said I could have just picked up the slip and went to the shop to claim for the warranty meaning the authenticity of my slip is not valid and this made me just lose it because now I am treated as a potential ******** because I do not have plumbers tax invoice and cannot get through to the plumber.