Philippines passport holder currently working in Bangkok and planning to get Chinese S2 Visa

First, I am a Philippines Passport holder. Second, I'm currently employed here in Bangkok, and third, my family lives in Shanghai and work there as well. At the end of this month i'm planning to go to Shanghai and visit my family only for 5 days. I have all the requirements listed in the internet for S2 type and i already went to the PRC embassy here in bangkok to check if all my requirements are good. Everything is ok. It's just they keep on asking me about this "invitation letter for touirst from the government with the stamp of Tourism department of PRC." They said for some nationalities they need this letter first before it can be approved. I already have my round trip ticket but i don't have any idea on how i can get this letter. They told me i could ask the travel agencies here in bangkok but when i asked several agencies, they said they don't do it. I hope anyone could help. Thanks a lot.