Dear Sirs,
We thank you for your letter dated 11 Nov 2012.
As items Nos.1 and 2 of your order were not ready with us and since these two items formed 75% of the total value of your order, we could not execute the order earlier. However, the goods have now been dispatched on 10th Nov and we hope you would have received a copy of our invoice which was sent separately on the same date.
Yours faithfully,
For GHJ Company