Why does mine say this?

"New" iPhone?

• Is the iPhone truly new, having arrived in a factory sealed unopened box?
• Was it sold by Apple directly or an Authorized Apple Retailer?

If both the above are true, you have fourteen days from the original purchase date to exchange the iPhone.

Otherwise:

About genuine iPhone batteries - Apple Support

If it's a brand-new phone, there is something wrong with it. Did you buy it from Apple? If so, you have 14 days to return it. Take it back and get a new one. Do not go through the Genius Bar.

Try to get your money back.