Cannot renew my F visa twice

Hi, I ve entered into China (Shanghai) on June 29th with a F one single entry valid 3months with 30days of stay. My company helped me to renew it and I have now a resident permit until August 29th.
As I am supposed to stay until September 29th, I asked my company to renew apply for additionnal 30days but I ve been told they cannot since the new policy in July 1st.
I dont understand why I cannot renew it and I need to leave Shanghai and spend one week in Singapore to apply for a new one. Moreover since I cannot wait for a new letter of invitation from Chinese authorities I cannot apply for F but L this time.
Could you please explain why I cannot renew twice my F and need to apply outside China? Thanks.