Apple India — phone reject in care

Its just been 50 days i bought my phone.
The display strucks too much & phone start to work automatically
I showed my phone to care they saw the problem live then they updated my phone & gave me back telling that again if you have problem we i ll replace. The next day again display started to struck then they took my phone & now they are telling that my phone is already opened & all like that. They are like there is some fingerprint on phone display inside so its opened & not covered under warranty. Why will i give my 2 month used phone anywhere outside for service they dont understand my problem
F1 solution in chetpet chennai