I took my van for an alignment. I was told the chamber is not adjustable. Is this true?

It is partially true.
There is a camber adjustment kit......a plate that is installed on the top of the strut assembly....which permits the camber to be adjusted in 1/4 degree increments.
Installation of this kit would require that the strut assemblies be removed to and re-installed with this new top plate.

The camber should only need to be adjusted if the vehicle has been damaged, such as in a accident.
So, unless something happened to make a significant change in camber, it is not something to worry about.

Wiswind, thank you!