Visa for Turmenistan residence

Goodmorning, I am a Turkmenistan residence, and now i am studying in Bangkok. I was planning to apply for visa to China in Bangkok, but it requires proof of legal stay, what does that mean? I can not get Proof of adress, because for that immigration office need 90 day stay stamp, bu as i am traveling every 30 days, i can not get that 90 days report, even though i have a 1 year student type. So what should i do? How can i apply? And how much does it cost? Thanks! Adam!