Application rejected because invitation letter is needed

Hi I am indian Passport Holder working in Thailand from past 7 years, right now i need to visit to china i had applied in Chinese embassy Thailand but they reject the application by saying that need Invitation letter as i am first time visiting there they need Invitation letter from PRC

is anyone can help to provide there contact details or email address. or how i will apply for that letter? please advise.
Thanks
Regards
Yuvraj