[Date]

[Addressee]

Dear [Name]:

re: 

This is to acknowledge the receipt of the above referenced 
order and to inform you that there is an error in the shipment. 

The merchandise I ordered was [describe], yet the merchandise 
I received was [describe]. 

Upon receiving your instructions for the return of goods, I will 
send the incorrect merchandise back to you. 

I would like to receive the correct merchandise as quickly as 
possible and will appreciate your expeditious handling of this 
matter. 

Very truly yours,