I had to revise your paragraph quite a bit in order to correct and improve it. If you have any questions about my revisions, just post them, and I'll explain.
Because they are now using single glazed panels instead of double glazed panels, they will not be able to complete this work by [date], which is the date indicated in the status report that I forwarded to you on [date]. The supplier needs another fourteen days to complete the work. Therefore, this work will now be finished by [date].