SA Post Office not delivering mail on time

I received a letter in the mail today letting me know that I have a piece of registered mail at the Silverton Post Office for me to collect. But the letter is a final notification (this is the first letter I am receiving with regard to a piece of registered mail waiting for collection) and states that I have until 09/10/2015 before the Post Office will send the piece of mail back. So I receive the letter a MONTH after the letter has already been sent back to the sender. This is obviously an important letter since it was sent with registered mail. I have no idea who the sender of it is and I can not get hold of Witspos (which is the return address on the piece of paper) to ask about the whereabouts of my piece of mail. This is not acceptable at all!!