OnePlus India — damage by customer service center

Address:	New Delhi, Delhi, 110021
Website:	www.oneplus.in

Bought oneplus 3 phone in july 16. Within a year, camera focus failed and earpiece low volume issue. Got promotion sms from oneplus stating that service charge for repair work is free and 10% discount on parts. Later on came to know that oneplus wanted to train their new manpower on repairing phone's and accordingly advertised the offer.
I took my phone for repair to oneplus service center at south court, saket, new delhi on 16 jun 18. They inspected the phone and sent my phone to the repair team. I was not informed of any more damage to my phone.
After the repair, i noticed my screen top portion is detached from the body of the phone. I informed the person concerned and was told that i should cover the phone using back cover. They also brought out that this problem existed before. Inspection before the repair by the trained customer service center person did not reveal any damage.
To repair this i was asked to pay 7k to replace the whole screen. This is due to replacement oriented servicing rather than repair.
I tried taking up the issue with head of the oneplus but nobody seems to bother.
I would like to complain on the sub standard product, poor service network (Only 3 service centers in delhi), replacement oriented servicing rather than actual repairs thus charging very high, not accepting manufacturing defect.
My phone internal parts are exposed now and would lead to damaging other parts subsequently.