Q: automatic shutdown of iphone 6

I have problem of automatic shutdown of my iphone 6 . I brought this phone in January and within 4 months it is giving me problem.

I am regularly doing chat with apple person.They restored my iphone twice still facing same problem as there is no solution .

They are not even ready to replace my iphone is in warranty period .

My iphone has problem of automatic shutdown while using any application it get shutdown at 48%,so when i connect to charger it will show me 48% then how come it get shutsoff i dont understand . I am trying to explain them from 25/4/2015 .

They are not taking me seriously everytime telling me to diagnostic test .

They say battery is in good condition.But no its not some problem is there it gets shuts off any time while i am on face time or facebook or i am on call and it shows me symbol of low battery. Sometimes if it goes to 20 % it gets shuts off doesnot even wait till 1% .

I want to replace my phone .I am tensed that i am in loss . Give me solution to direct contact email i.d.