RESPONDING TO JUSTIFIED COMPLAINT: INCORRECT SHIPMENT
I want you to know that we value your business greatly. Please accept my apologies for our incorrect shipment to you on [DATE, ex. Tuesday]; [STATE WHAT YOU WILL OR HAVE ALREADY DONE, ex. I will immediately ship the balance of your order and arrange for the incorrectly-shipped items to be picked up on delivery. Your order should arrive this Friday.]
I sincerely apologize and hope that you will call me at XXX-XX-XX if there is anything I can do to minimize the inconvenience this has caused you.