Just because your first email meets with a rebuff, there is no reason why you should not
a) challenge the points made in response
b) write to another main board director for a second opinion
c) involve a third party such as trading standards or an official watchdog
d) continue corresponding until the company concerned gets so sick of you that they finally surrender.
If you remain cool, polite and determined, the fruits of your efforts will often emerge from the most protracted of disputes.