Lost package – Who refunds?

Simple question but not sure of the answer

Bought UPS shipping through Amazon

Customer claims over a month later they never received. Tracking says it “The delivery of your package has been rescheduled based on your shipment instructions for the carrier.” The package never did deliver. Customer claims they didn’t reschedule it.

I also didn’t reschedule it. As the package never arrived should I refund this or should I have the customer file an A-Z claim?

Thank you!