In the Layers panel, select the mask (not the image). Then unlink the mask by clicking on the chain symbol between them.
I tried that but when i unlink the mask, even with the mask selected when i try and resize it resizes the image not the mask.
Is there a way to unselect the image? Seems only options are or both select or just image.
Maybe a corrupt preferences file. To reset to factory defaults, hold ctrl + alt + shift when launching PS. You'll get a confirmation dialog. Remember to save out your custom actions, brushes etc (they'll be wiped).
Unlink the mask from the image and select the mask by actually clicking on the mask thumbnail.