I have a valid invitation letter and I am being asked for a visa notification form for interview.

I need a tourist visa to China and the personnel at the Chinese consulate in Lagos Nigeria have refused to give me a date for interview because I do not have a VISA notification from from Chinese govt. I am going fro only 5 days and I have my ticket and hotel reservation evidence. How do I convince them that I am not doing business with any body but just going to attend a conference. I have been to China with a visa before and spent 5 days