After checking the document, seems we cannot refuse any charge base on FOB terms.
After checking the document(s), it
we cannot refuse any charges
I put the (s) in parentheses because I'm not sure whether there is only one document or if there is more than one document.
I don't know whether it would help to state more about the FOB terms (as in whether the terms are FOB "shipping" or FOB "destination"), but that's not really a question of English grammar.