my old iphone was stolen, I bought it over a year ago and need to prove that I bought it. so how do i get my purchase history from over a year ago?

This phone was stolen by a friend of mine from me, I have no idea where they are or if the phone is even actvated( i was using it as an ipod). I have used the find my iphone app to try and find it, but its not near an internet conecton so it can't find it. I have locked it with the app as well as seding it a messages saying this iphone is stolen, please call #. I need to prove that I bought it in case his mom turns it in to apple or verizon.