Rafi From Kabul, Asking for China Visa

Dear Sir, This is Rafi from Kabul Afghanistan, recently we bought some machinery from China, the company which we bought the machine from, sent me invitation letter because I should be trained well before the machines are shipped. I have the following documents.
1. an invitation letter from duly authorized unit
2. the original and photocopy of your company’s business license
3. residence proof and its translation copy
4. bank deposit certificate with a balance of more than 4000 dollars
5. a non-criminal record authenticated by Afghanistan Foreign Affairs Ministry and its translation copy
6. round-trip tickets.... but still the visa is not provided.
what else step should I take in order to get it that is really much important for me.

Thank You