Dear :

I am writing with regard to your inquiry of [date] about the [goods] you returned to us [time] ago.

Unfortunately, after checking our records carefully, we find that we have not received the goods you returned. Would you please contact the shipping company to find out the whereabouts of the goods? We will be happy to send you a refund, but we cannot pay for returned goods that we haven't received.

I will of course be glad to assist you in your investigation. If you send me the name of the shipping company, shipment number, and other details about this shipment, I will help you to trace it.

Hope to hear from you soon.

Sincerely yours,

[name]

[title]