Tourist visa application

Good morning. I would like to know the cost effective and the fastest way to apply for a visa.I am a South African however currently based in China as a student. I am studying at Peking University.
I had a terrible experience when I tried to travel to Vietnam on Tuesday (15th )for 6 days holiday and I was turned away at the Hong Kong airport whilst trying to check in. I was told that I needed a visa after a friend advised me that I do not need it. I had already paid for the hotel and my flight and I could witness my flight departing in watch because it was too late to do anything. The experience left me traumatised as I was looking forward to my holiday. I have since moved my hotel and flight booking to the 12th of June and coming back on the 17th of June. Kindly advise me about the procedure and all the reasonable costs involved preferably in RMB please if you can .
Thanking in advance.
Queen