Unsatisfactory on goods

I would like to express my extreme disappointment for Cashbuild south Africa and Superline kwik Geysers manufacturing company. They claim their geyser lasts for up to 5 years. So back in 2020 I purchased my first geyser for my mother's house in Soweto. I went to Cashbuild to make the purchase, upon purchasing the sales man explicitly told me that I need to make sure that this geyser is installed by a certified plumber and that I should insure to keep the copy of his certificate and also keep the purchase slip safe incase our geyser multinations either leack or overheat, when that happens we must inform the shop immediately and they will return to the manufacturer for replacement. We are in May 2024, 3 and a half year later our Geyser started leaking, we called the store first to inform them about the leaking Geyser, then they advised that we should take pictures of the installation and bring along the purchase slip. I went on the 08 May following up on our telephone conversation. The manager then asked for a serial/ model number I then tell him I don't have it. He said the serial number was on the Geyser when in was delivered and installed and it was supposed to have been taken to record. Now I am confused as this is the first time I hear of this. What actually makes me angry more is that, they advised us to install it outdoors for incase of leaks we won't have to experience flooding in the house but also failed to also tell us the most critical information to remove the serial number sticker or record it somewhere because obviously due to whether conditions the sticker will wear out. I mean this is 3 years later. He the told me that the plumber was supposed to have known that? No I disagree, the plumber doesn't work for Cashbuild or Superline to know their policy when it comes to installing Geysers. He also asked for a booklet that came with a Geyser, I asked what is that... He took me to the Geyser isle and opened one on the plastics and pulled out a booklet that Superline will require when we submit for a claim. I was confused again, why? I never saw nor heard of that kind of a booklet when I purchased that Geyser and when this Geyser was installed we didn't see this booklet and there is absolutely no proof that it was on the plastic. He went on telling me ho important this booklet is and showed me the information that was supposed to be recorded when the Geyser was installed. Wow okay.. What is happening now because I feel like a big Fool. Sir whatever you are telling me is completely new and how is possible again to miss such critical information if you claim we were told about all of this. I kept my end of the bargain by ensuring I comply with what I was told. I kept my purchase slip and also I hired a cerfied plumber to install this Geyser. Cashbuild acted unprofessionaly and mislead us with half baked information regarding the Geyser warranty. If the information they claim they provided where is my signature where I signed and agreed and understood on the terms and conditions of the waiver. They also failed to take responsibility on their side by not investigating who was the salesman who sold us the Geyser and hear from him why he did not provide us with the correct information. They were quick to tell me in my face how I won't claim even though I told them my story. My consumer rights were infringed due to unprofessionalism and people who don't know how to do their job.