Conflict with the aliexpress seller, pleas help

Seller sell lens as 4mm focal length, but in description there is viewing angle data for 3mm lens and my measurement and these web site show 3mm. I want 10$ money back, because I'm searching for good starlight lens from 4 to 6mm and realy don't need 3mm lens. Seller reject my request because product is as in description. More about these lens and my situation in these thread

It's look like that somebody don't know these fact

1/3 type have 1/42333" diagonal, even at Apple.
What do you thing, who is right.

I can't say if your or the seller's calculations are 100% correct but I don't believe the seller is knowingly trying to mislead buyers. I have various 4mm focal length cameras and there is always some variation in the field of view among different models. If the 4mm lens you have isn't what you want, save it for another project and purchase the next size.

Of course there are differences, because the cameras have diferent sensor. 1/2 "camera has double viewing angle than 1/4", but focal length is exact value, last exact value and we must fight to stay relevant.