A registered letter undelivered

We want to sell a house and send the documentation a month ago from Overseas to South Africa.<br> The last couple of weeks we see on the tracking system that the letter is in South Africa, but SA Post is too busy to handle it, because they have backlog.<br> <br> The foreign Post office talks about 8 - 11 working days, but this doesn't care the SA Post.<br> What can we do to get the letter and close the deal?