Dear :

We have sent back by UPS the [goods] that were mistakenly shipped to us on [date]. The items we ordered on [date] were [items], not [items]. Please check our Order #.

Enclosed is your Invoice #. Please let me know as soon as possible how you would like the mistakenly shipped goods returned. Meanwhile, please send us immediately the [items] we ordered.

Sincerely,

[name]

[title]