Vietnam form e mainland company can check the third party in

We are Shanghai Import and export company. We have invoice goods exported to Vietnam. Now our company can't make form e certificate of origin, and then we find an agent to do it on the Internet. The first column of form e certificate of origin shows the head of the agent company, our company's head shows the description of the goods in the seventh column, and now the customer wants us to make the form e certificate of origin form E. the third party invoice in column 13 is checked. He said that only in this way can they normally clear customs and duty-free. However, our agent said that because we are a mainland company, we can't check here. Column 7 must show the offshore company, so what should I do? The first ship will arrive at the port next week, and I'm still struggling with the customer for this problem.