Conyac で依頼された翻訳結果を公開

Even though it shows that the package has been delivered when I check the tracking information, I received a negative feedback from the customer saying that the package has not arrived yet.
The purchaser insists that this is because we are lacking some documents, but if that is the case, Japan Post Office won't ship the product so the documents should be fine.
It's evident that the fault lays on the purchaser's post office, not on me. Do I still need to accept negative feedback then?
If this is not an appropriate evaluation, please remove the feedback.

I don't know when the product will be returned to me so I'll make a full refund for your purchase.
After the product returned and I confirmed your payment, I'll ship the product again.