Buyer cancel the order, Amazon refund the money but shipment already ship out.

I received the email from Amazon- We have cancelled your order as per customer’s request. Below are the details of the order: Our problem is this order is already packed and pickup by post office at All the information on this order has been deleted including the tracking number. If the tracking number still there, I can have the post office return the shipment. Today I received another email with the same cancellation but shipment also already ship out. It will be great if the seller can handle buyer cancellation of the order. Any suggestion or help will be greatly appreciated.