Bests & Worsts Reviews from Amazon

I just put my chair together and the ball is significantly smaller than the one pictured on the site. It doesn't touch the backrest or the front constraint and it is about 5 inches shorter than the one pictured. I feel like I am sitting on the ground and the ball is not held in place very easily. A lady in my office has the exact same chair and same brand but her ball is a lot bigger than the one I received. I would still love to find a ball chair but am at a loss of where to look, this is the second one I have ordered and received with a ball that is too small. I took pictures of my chair and did a side by side comparison with the one featured on the site and would love to upload it but am unable to.