Paytm Mall - Paytm box pack item faulty not taking a return

I purchased a coolpad phone from Paytm Mall which came to me faulty at box packing level where the microphone is not functioning properly. Every time we have to shout to put our voice across. On complaining, they say I need to get a job sheet from the coolpad service centre. When I called the service centre of coolpad they denied to give any job sheet for this case and updated that this needs to be handled by Paytm itself and we will not provide any job sheet for the same as it is a box pack fault. Paytm is denying to replace the phone. Need your support to have my phone in working condition through Paytm.