about business visit to china

i am chief executive officer of ontheway empire enterprise, here in Ghana. and i want to visit china for business reason, but my problem is this, the company invited me with their stamp on it but on arrival at the security check point at the Chinese embassy, i was told by them that, they required official stamped invitation letter, i want to ask this, what invitation is acceptable by the Chinese embassy and secondly, whom can help me obtain this invitation letter. i am very desperate about this and need help now. thank you and await responses.