how can i obtain a business visa to China in Bangladesh?

I have visited china three times....with L visa...now my supplier in china applied for my invitation from their local government...for business visa..but they are asking for F visa of previously visited...but in past,they have issued L visa,so how can i submit local govt "F" visa record? they are not interested to listen anything..said supplier...that maens,any new person can't get F visa if don't have now? pls advice me...