Product under warranty and not covered

DEWHOT Gas geyser is under warranty (10 months old) and I have another Paloma geyser installed at the same time by certified installer. Both geysers are about 20 to 30 metres away from the main cylinder.

DEWHOT geyser was great but there was always some fluctuation of water temperature (some time it is really noticeable and some time it isn't). The geyser stopped working two days ago and according to Dewhot CT, it was gas issue as some of the oily residues entered into the gas chamber. It makes no sense based on various reasons -

1) Only 2 cylinder of 48kg gas were used and none of them were delivered or ordered during lock down. These gas comes from distribution centre directly. 2) distance in between the two geysers are identical and they are 20 to 30 meters away from the actual cylinder 3) temperature fluctuates - even after the part was replaced two days ago, then water temperature was not constant or consistent. I raised this with technician on site as well but was brushed off. It was registered at 45 degree celcius for a period of time and it would not go up even it was set at 55. It was the same issue when the part was replaced and I advised the technician that water temp was definitely incorrect by feeling with hands (I can put my hands under that water) 4) Paloma didn't have any sign of residue even though it was used less than Dewhot 5) I was charged part under the warranty as Dewhot claimed it was not covered by warranty and it was the gas fault (all speculation at this point). And according to the technician that I was meant to be charged for labour as well and it was a favour that they did not charge that on the invoice. I had to pay that invoice immediately while he was on site. R600.00 instead of R1200.00 6) So the gas issue apparently is my fault and when I queried if there is any way to service the machine due to these residues. The reply was that they are currently working on a filter but it is not yet available. So it means there is a possibility that I will need to pay DEWHOT R1200.00 every few months for this defect 7) They are not keen to replace the geyser under the 12 month warranty as it was my fault that gas has done damage to their geyser. ???

So I guess it is like buying a car and you cannot service the car due to none of the parts are removable. So when there are issues with your car and your warranty / motor plan is non and void. ... I am supporting SA product and business as Dewhot came highly recommended. However I don't think I will ever recommend their product ever based on this experience and it will cost me a lot more in the long run than the Paloma on maintenance. They simply do not have the after sales service.