The 28 days might not be in the letter, it may be in the web page itself - I don't really recall but here is part of the message I got:
(Timely and efficient processing is important to us. We receive an enormous amount of correspondence daily. Although we would like to respond to all of it, we recognize that it takes resources away from finalising applications.
To minimize the impact that replying to enquiries has on processing times, we respond only to correspondence from people who have already applied for a:
Ø permanent resident (immigration) visa
Ø temporary resident (visitor, temporary work, study) visa or permit.
Kindly note that we are not able to acknowledge receipt of documents, changes of address, and other case-related information. We can assure you, however, that the new information you provide will be placed on file.)
Did you get anything similar to this??