Dear Mrs White

I was very concerned when I received your email today stating that the central heating system in your home has not been completed by the date promised.

On referring to our earlier correspondence it seems that I had mistaken the date for completion. The fault is entirely mine and I am very sorry about this. I realize how much inconvenience my oversight must be causing you and will do everything possible to avoid any further delay. I have already given instructions for this work to take first priority. Our engineers will be placed on overtime to complete the work. These arrangements should ensure that the work is completed by next weekend.

My apologies once again for the inconvenience. Please call me personally if you have any other questions.

Best wishes

Ed Smith