The invitation letter should be issued by a authorized Chinese organization. You can ask the Chinese registered company to give you an invitation, If they don't have the right to issue an invitation letter, they will try to request a letter from the authorized Chinese governmental organization.

hello again,
sorry for so much troouble, can u tell me how much usually it cost for at 6 months F visa?
Thanks

Visa fees for Philippine passport holders: (peso)
( 4 working days) 3 2
Single entry visa 1400 2500 3100
Double entry visa 2100 3200 3800
6 months multiple 2800 3900 4500
12 months multiple 4200 5300 5900