Poor service and hardware reliability on mobile phone

My Samsung Galaxy S7 was 23 months old when it began restarting itself after a software update. I handed it in at a reliable repair store which tried reloading the software multiple times over a week's period in various ways. Their conclusion was the pc main board had a hardware failure and needed replacing. They do not open the phone to replace the board, so recommended me to take the phone to Vodacom repair store. The same day I handed the phone in at Vodacom repair store and that afternoon Vodacom contacted me with the same pc board hardware failure reason. However, the 2 year warranty period from Samsung expired 5 days ago while the phone was at the previous repairer and I would have to personally pay R6325 to repair the phone. I called Samsung insisting that the phone was still in the warranty period while at the first repairer and should be repaired at their cost. However, they refused as their policy only applies at their approved repairers and the warranty expired by the time I handed it in at Vodacom Repair. This is not reasonable and fair customer service as the fault was identified at a reputable repair store while the phone was still in warranty and the same fault identified in the same week by the Samsung repairer. Since then I have read other reports on Samsung devices failing after a software update damaged the hardware. An expensive flagship device like the Galaxy S range should not have hardware failure within two years of manufacture. The phone was in a Samsung flip cover protector all the time and never experienced physical damage to cause the hardware failure. Poor support and service from a company that I have invested 5 mobile devices over the past few years. All I now have is a very expensive paperweight and doubts on upgrading to any other Samsung devices.