Invoice for iPhone X

I purchased iPhone X on 09/12/2017 from Apple stores ,Lincoln Road,Miami.

I am trading it for iPhone 12 mini.

Retailer, Inspire, Nagpur, India, now wants the INVOICE COPY of my Purchase. I am struggling for last 2 days but no one is willing to help though I contacted Miami store, Apple Singapore, Apple Banglore ( India). We never thought that Apple will give so much trouble to a Senior Citizen ( I am 65 years old) and loyal customer ( In our house there are 7 Apple products). I l spent and wasted USD 65 yesterday on phone call to Miami stores last evening.

If you are sincere person please help.

DINESHKUMAR K KAMBLE

Nagpur( India)