Help!!!

I am a brazilian citizen residing in Belgium, i came from China to Belgium about 1/5 year ago and i will get married with a Belgian citizen in october this year...
I am busy gathering the documents i need to marry her and so far all the documents are ok!! But since i lived in China for 2 years before coming here, they are asking a certificate of non marriage from China, in other words to say: I have never been married in China, How can i get this certificate??

Thanks