how can i obtain a tempory visa to get to china for work?

my flight has been booked for 16 August from South Africa. I am going to work at Jining Confucius International School. the problem is i cannot change my flight as i lose the money totally. what happens if the delivery of the invitation and permit do not arrive in time? is there anyway we can ask the school to send to Beijing where i will be visiting from 17 August to 20 August and get the documents and passport corrected? what can i do ? please please help. can we get a letter from school for now in South Africa or will i be allowed to enter Beijing and obtain there, or can i get the school and sort out with 24 hours or so?
i would appreciate feedback that is legal and doable from South Africa