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Located Source Of Problem
LOCATED SOURCE OF PROBLEM
After some investigation, I believe that we have found the source of the problem that led us to our misunderstanding on (date).
When we received your purchase order for (quantity and product), we were unable to fill the order for immediate delivery due to (explanation for delay in delivery) Our letter informing you of this delay and requesting your instructions was mailed to you on (date). We did not receive a reply and proceeded to send a follow-up letter to you on (date).
We have been able to make delivery to you since the (date) but felt that since you had emphasized "for immediate delivery" on your purchase order, we should wait for your authorization before shipping.
I can easily understand why you were so upset with us (day and date) if no one made you aware of our correspondence.
We have always appreciated having you as a customer and hope that we can continue to provide you with our products in the future.