Apple India — worst service

Address: Bangalore, Karnataka, 560035

I bought an iphone 8 last december. Till now i have given thrice in the service centre. It’s getting stuck always. The screen is flickering. I’m giving in service centre they are just changing software and returning back the device saying that device is kept under observation and it is working fine.
But it’s repeating. Last week i gave again and they changed the software and said same thing that it’s working fine in their observation. But i was asking for device replacement which isn’t happening. I bought it for 58, 000. If the same problem repeats after 2 months. I should pay half amount for device replacement. I got a faulty device when i bought. It’s not my mistake why should i end up paying 30, 000. It’s their responsibility to replace.
Not at all satisfied with apple service.