OnePlus India — One plus 7t pro display watermark impression issue and lagging issue

I have bought one plus 7t pro from amazon on 01/11/2019 and it has speaker issue then one plus has issued a replacement of the phone and i got the replacement product on 19/11/2020 now the phone is having lagging issue and the display is sudennly showing water mark ofsome applications on background i have reset the phone but i am not able to remove the watermark on background and one plus is not respondind me i want refund for the same