If you are the buyer why did you receive a letter from the bank? The bank would be working with the seller and their agent to keep them informed on the status of the short sale package. You need to be in touch with the agent representing you and if you worked directly with the listing agent then you need to call them. Unfortunately short sales do take time and cause confusion. Each lender works differently.
I know this is frustrating, but this is the scenario with short sales. If you are being represented by a Realtor, have they tried to see why you have not been contacted?