Dear …
RE: Wrong Item Shipped
We are writing to you in response to your letter dated __(date)__ wherein you advised us that you received the wrong merchandise. We have now looked into this matter and found that we did make an error in our shipping department. Please accept our sincerest apologies for this error.
We are currently expediting shipment of the correct __(name of item) __ to you. You may expect to receive this in approximately __(length of time)__. In the meantime, we ask that you kindly return the __ (name of wrong item) __ you received, along with a copy of receipts for your shipping costs. We will gladly reimburse you for shipping costs of the returned item.
Once again, please accept our apologies for this oversight and any inconveniences it has caused you.
Yours very truly,