How to get E-receipt for purchasing iPhone

Hello Apple Community,

I purchased an iPhone 6(Gold 64GB) in Hong Kong Causeway Bay Apple store about 1 year ago. The iPhone had been lost and now I got it back. However the problem is, when I renew the iPhone with the latest iOS version in iTunes, it keeps asking me for providing an account and password which I never used before.

Right now I'm in Shanghai China. I called local Apple service but they told me I have to provide sales receipt for unlocking my iPhone. But unfortunately, the receipt is lost.

I understand that I must proof that the iPhone is mine. For getting e-receipt, can I provide the credit card which I paid with for this iPhone? Actually, I purchase 2 iPhone and 1 Mackbook in Hong Kong Causeway Bay Apple store at same day with same credit card, and I did receive an e-receipt for the Mackbook.

Any chance I get the e-receipt for my iPhone 6? Is there any other way to unlock my iPhone?

Thank you.