Your handset seems close-enough to a "DOA" if it failed so quickly. Swapping it for another new one should be routine. Scratches don't matter when a phone is returned for being DOA. Furthermore, when a phone is new enough, you can return it for any reason, such as it having a "bixby button" (I wish I had returned my Samsung S8 for that reason years ago!)
Please consider to reverse the charge via bank after giving Xfinity mobile one more chance to waive the charge and send you a new phone, maybe a different/better model that you will like better.
Regardless of whether xfinity-mobile or your bank reverses the charge, xfinity-mobile may yet try to retain your business and offer you new service with a new handset and possibly a double-secret "give us another try" discount that is offered to customers who have had early failures with a new phone.