Amazon India — regarding giving me an old and used mobile phone instead of new one

I received an old phone which was packed properly like new and i bought it from amazon on 15th of june 2019. Due to some problems in it i went to service centre to get the problem fix but they denied to do the service of it and said that they need the original bill because as per their records that phone was in use from november 2018 while i bought the product on 15th june 2019 and it was delivered to me on 19th june 2019. And now when i am asking the amazon to fix it they are asking me a service denial letter and the service center is denying to give it.