Susie924, I guess I'm operating on a significant time delay...
Did you finally get your mouse problem resolved?
I don't know why the old brain waited until now, but it occurred to me that you may have missed something.
Maybe it's because I'm starting to have the same problem, which I'm about to fix. (had it before)
You said, you had "cleaned the ball and checked for dust inside the mouse."
That won't do any good.
Inside a standard mouse you will find three little rollers that make contact with the ball. In mine they are black plastic.
A very fine layer of dirt and grease can build up on those rollers and be almost undetectable. This will produce the exact problems you were having.
What works best for me is to take a few Q-tips, some alcohol and clean the rollers.
Works every time.....
Hope this isn't too much after the fact......:)