Magic Mouse - Can click and use top scroll but optical won't move

I have a Magic Mouse and can click and use top to scroll and click but optical won't move.

I've tried:

- A wired mouse and my track pad and both work fine

- Replaced batteries

- Cleaned contacts for batteries

- Removed mouse and re-paired

- Cleaned the optical parts

- Tried various surfaces

And nothing seems to work.

Very bizarre that I can still click and use my finger to scroll pages up and down but the physical movement of the mouse won't do anything.

Any help appreciated