China Consulate won't accept my Tourist L type Application!

Hello, I am resident of US holding a Nigerian Passport. I went to the China embassy in NYC to apply for tourist L type and they said they do not issue tourist L type to individuals from my country. I used an agent, they also got rejected. Please advice or provide info on what i can do to get a visa to china. My ticket is already bought. My itinerary is to fly into hong kong, spend a 3 days and then fly to Shanghai to spend another 7 days and then back to the US. I have also sent my application to hong kong for an entry permit, hopefully that gets approved. I have invested a lot of money and time into this and my ticket is unchangeable /non refundable. What should I do? Any recommendation on a different way to obtain the visa?