My Rear Camera won't focus iPhone 6 Plus

HI guys,

My iPhone has a problem that its rear camera won't focus at all. However, i already tried every solution suggested in this community, of course, the problem still here.

The last method is to have a service from Apple. Here is the problem.

I bought my iPhone in Thailand (where i live) in third party shop. All I get from this shop is a brand new iPhone6Plus with its box(sealed).

but the phone is from US, which cannot get a service in Thailand, because Thailand doesn't have an official apple store.

So, i asked US Apple Staff how to sort this thing out. He said i can go to anywhere in the world that has an Apple Store.

However, I went to HK to fix my phone. They said that i need a receipt to get a service. They fear that the iphone i bring along is stolen one.

The question is, can i bring a phone with its box to get a service there? because the stolen device shouldn't have its box right?

or i have to use this phone without rear camera forever??