How to get end user to guide the development?

[eluser]tomcode[/eluser]
You have a human problem, so :

can't You ask someone (responsible of the effort produced) how to act in such a situation in Your company

or :

explain Your situation to Your collegues, ask them for help

Do not code before You haven't established a satisfying communication flow.

EDIT : You need to be firm, stick to what You consider neccessary, be well prepared