Apple India — refused to repair iphone under warranty

Address: Ghaziabad, Uttar Pradesh, 201002

Website: www.apple.com/in

I purchased iPhone 4 months back and then one day it stopped getting charged up. I bought a new charger but still battery level didn't go up. Eventually it got switched off because there was no more battery life left.
I submitted the phone to service centre and they say its a moisture damage as headphone jack and charging port shows corrosion.
I asked them i didn't spill any water on it. Their reply was mositure in the AIR could have caused it.
Now they are asking for the amount of a brand new iphone to replace it, as it cant be fixed by them.

As a consumer, it is not all acceptable as my device is under warranty and i expect it to be fixed, even if i have to pay the labor charges. but asking for the amount of the entire phone is lawfully wrong.
When i called customer care and asked them do i need to carry my phone in a airtight pouch to avoid moisture, reply was YES.

I need my grievance to addressed.