No service on 8 plus

I have had my iPhone 8 plus for only 16 months now,I havent dropped or done any physical damage to my phone. It was working perfectly fine and all of a sudden it was showing no service. I thought there was some issue with my carrier, I then inserted a different sim but nothing changed. I then updated my phone to ios 12.4,still no service, I reset my phone to factory settings along with the network reset. Since it didn't work I then restored my device using iTunes on my Mac. I got the network back for almost 10 hours but then again it started showing no service.I was suggested to follow the above steps by the customer care executives, they were helpful at first but then couldn't solve my issue. I am really gutted now I have spent more than 55 thousands Indian rupees to buy this phone Its not even been 2 years and I am facing this. I went to the service centre they are saying I have to replace my phone for 40 thousand Indian rupees, which clearly doesn't make any sense to me since I have not got a single answer or explanation as to why this happened and clearly I haven't done anything to damage it in anyway. I am pretty sure there has to be some solution to this issue and I would like to request you to help me out.