Faulty screen?

We bought new a over the bath shower screen and fitted this ourselves, after a couple of days the pane of glass fell out into the bath, the company says the screen was damaged in transit, but we now know that the screen attatchment has got no sealant holding the glass to the fitment and was only being held in by a plastic peice, we still have the screen and packaging , but we are taking this further and need to prove that this was faulty and not down to being fitted.