Have you setup Face ID in settings you have to setup again on a new phone ?
https://support.apple.com/en-gb/HT208114 Apples help if needed
Is your phone brand new? Did you get online? If the answer is yes to both, then I would return it to where you bought it from if you've already tried resetting it via settings. If you bought it from a high street store, ask them to exchange it for you.
Just in case, this is from the apple website.
Hope you get it sorted.
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