Apple - i phone not working

i have purchased my phone on **-**-**** from flipkart and on july-**-**** my phone automatically turn in dead condition around ** pm in night while talking ,next day i went to authorized apple service center there i show my phone they checked my phone and agreed to sent my phone to banglore for further process after all the formalities they have told me to sign on job sheet i have asked them that can i write something on it they told me yes you can there i have written that "i want to replace my phone dont want any rearing on it" then that attendant told me that you cant write this on job sheet then i told her that its ok you can overwrite or you can prepare another job sheet for me then she replied me that i have to ask from my manager i told her that no issue you can ask then after * min she came and told me that we cannot accept your phone because you have opened this phone anywhere outside thats why we cant accept your phone i have told her many times that why i will go out side when my phone is in under warranty condition and why you are saying me now that we cant accept this phone before * min you are ready to send my phone to head office banglore and now why you are refusing to do this but i didnt get positive response from them and they have returned my phone to me then i call to apple costumer care and flipkart tean also but no one is there to help me on this both are going with service center team.
my simple question is that when my phone is in warranty period then why i or any one else will open it outside .