Dear

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      [specify]    , while the
merchandise I received is    [specify]         .

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

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