Is it mounted when you have this problem?
How close to the rear of the scope is the back ring? If it is too close to the adjustment knob, it will clamp the barrel that's inside the scope which adjusts the parallax.
If unsure, remove the top of the rear ring and try it again. If still unsure, take it out of the rear ring entirely and test it.
If it still does not move, send it back for repairs.
Ask me how I know....