Apple India — No action against the damage done by the service centre

Address: 122002

I have submitted my iphone 6s at the TRESOR SYSTEMS ( Service Centre) at Gurgaon. While submitting the phone there was no problem screen bubbling, but when i received the phone, the problem of screen bubbling was there. This problem was not from my end, something wrong has went from the service centre side. I have asked them to resolve the problem but they are making excuses and are not ready to accept that this there fault.