Bi-fold Shower Door Problem

Parslee

Had a new shower fitted last week but the bi-fold door when it’s shut meets at the top and bottom but bows in the middle which looks like the seal is being stretched, the gap is nearly a centimeter, I'm sure it should be completely straight all the way down. The fitter doesn't think there's anything wrong with it but it looks to me like something's been left out in the middle of the door to pull the two bits together as it's so loose it makes a horrible noise when you open it. Can anyone cast any light on this as to what he's done wrong please it's cost such a lot of money. Thank you.