Xiaomi India — defective mobile phone with colour change

Had purchased a redmi8 mobile on 18.11.19 online through amazon.
When dialing any number, the centre of the display screen is showing faintly a different colour. I am afraid that there is problem with the unit bought. Please kindly replace it with a good unit. Is it an old defective phone given to me? I feel cheated. Yesterday the phone all of a sudden got hung too.