An example of an apology letter for an incorrect quantity of goods is shown below.
Dear xxx,
We have received your email of Aug 7, 2019 and we regret to know the short delivery of 5 dozens of socks against the order No. 5132. We are quite sorry for the problem.
After check, we found that it was the fault caused by one new worker’s carelessness in our dispatching department. However, we have already got 10 dozens of socks dispatched by DHL to you in the second day after we found this mistake. Five more dozens of socks in different patterns were sent to you as compensation. DHL confirmed that they will reach your office on Aug 9, 2017. Once again, we deeply apologize for the trouble caused to you.
Best regards,
xxx