My phone is stolen

Having the serial number and the purchase invoice will not help find your stolen iPhone. Apple does not track down lost or stolen iPhones for users. That’s up to the user alone. If the iPhone was, as you say, new and unused, you are probably out of luck. Make a police report. The standard warranty, of course, does not cover loss or theft. If you purchased AppleCare+ at the time you purchased the iPhone, two incidents of loss or theft is covered with a deductible.

https://www.apple.com/support/products/iphone/

Romeo999 Said:

"My phone is stolen: My phone is stolen, new and unused, I have the serial number, and the purchase invoice"

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Lock with Find My:

Was Find My enabled? If so, I'd say use Find My, and see if you can lock it. AppleCare does not cover lost or theft.

Loss and theft is not covered by Applecare plus.

You have to buy AppleCare plus with Loss and theft Coverage specifically.

It is not available everywhere.