I bought an iphone 7

Nothing we can do.

Whether this iPhone was originally lost or stolen, the original owner with a receipt or the person that last owned this can clear Activation Lock. Activation Lock is a theft deterrent.

Assuming you can’t locate the seller to release this lock or to refund your purchase, you now own an expensive brick.

The All Too Common SAD Reality of Buying … - Apple Community

Return it for a refund. A used iPhone or iPad should never open to someone else's account. You should get the setup screen for a new user as if it just came new out of the box.