The problem is VPN is now banned unless it's recognized by the state (must be registered). You can still try to use the underground VPN, but not guaranteed. The GFC knows everything in and out. It is one of the most acclaimed and sophisticated closed source networking system in the world. They can toggle on and off in matters of minutes. They have a huge work force monitoring their internet and censoring speech in no time.

Of course the Chinese government are aware of existing circumvention, but they still allowed them because they want to capture data. They let these circumvention to exist even though they have the brightest engineers in China working for them. I vaguely remember a talk from RealCrypto a number of years ago, someone presented how one could try to escape GFC by sending data over different protocols and then resemble by the recipient. It's an ingenious circumvention that is quite hard to decipher, until someone recognizes a traffic pattern, then Chinese government knows.