Student Visa to study Chinese in Guangzhou

I would like to study Chinese in Guanzghou. I am already in Guanzghou for almost the last 2 months and now I would like to stay here for another 3, 4, 5, 6 months or as long as it takes to learn Chinese. I have been in contact with many private schools but I have not found anyone who can give me information about how to process a student type and they say with just an invitation would be enough. Is it true? If not please, Can anybody advice me about how to process it?