1. This is a formal letter: it is, not it’s
  2. What are “the companies and their products/services"; Is “including MTR Mall, Property and Project" an exhaustive list?
  3. Avoid using " ‘s " after non-living objects.  Use xxx of yyy instead i.e. “the staff and stake holders of the MTR Corporation".
  4. Do not HESITATE
  5. “Please do not…on the date with booked insertion" should be followed by a period (.). “We shall…." should be a new sentence.
  6. Midnight means 12 o’clock at night. “During" midnight is simply impossible. It should be “during midnight hours".
In short, get a new advertising agency.