English requires you to practice using what you know, so you can listen and express your understanding of the words more confidently.
Try attend as many English CONVERSATIONAL classes as you can. Even better, befriend a westerner who actually lives in China. That may be a touch difficult given work commitments. Therefore, keep doing what your doing and go to English classes a couple times a week i you can, with a focus on Conversation.
Secondly, read books written in English. Your command of the language will improve more than you may think, as any good book actually published as a story requires intricate use of English language and expression. Those things.