The carrier's tracking indicates that the package has been delivered to the recipient, but your customer claims not to have received it:
T-Pop does not cover the shipment of a new package.
The tracking of the carrier is proof: if the package is marked "delivered" there is no possible recourse.
Often the package will have been dropped off at a neighbor's house or the customer does not have a standard box:
In this case it is necessary to recommend to your customer to go to the nearest post office (if the carrier is the Post Office), with his tracking number and an ID card to retrieve his order.
If the mailbox is not standardized or the package can not be deposited there (because it contains too many products), it also happens that the deliveryman deposits it at the nearest post office.
If the customer nevertheless tells you that he has not been able to retrieve his package, the decision is yours: you can tell him that once indicated "delivered", you are no longer able to send him a new order or you can decide to place a manual order at your own expense.