Geometry is the math that dictates this decision. it has been in use since ancient times when the greeks invented it. it is the same currently, as it was 25 years ago the first time i went to college, and the same in ancient times as it will be in the future,...your order stated the width was 24" which is the "horizontal" measurement.
the order also stated the "height" was 18" which is a vertical measurement. these terms have not changed in over 2 thousand years,..the order also "plainly" states the flutes to run horizontally on the same page that the horizontal measurement is specified. It should not matter mathematically whether the final print is considered upside down sideways or at an angle the flutes should follow the horizontal measurement specified in your order. You did not order an 18" wide print, you ordered a 24" wide print. If their employee cannot determine the difference between the two they need either to re-educate their employee and or dismiss him or her,.....any idiot with the slightest amount of common sense in the sign industry knows that coroplast signs usually go on coroplast sign stakes and or cinderblock rebarb stands on vertical flutes,..thus if they use the excuse they did it by the way it reads it is still null and void. they made a illogical assumption and the math here doesn't add up. Simple answer here, they screwed up . Please note the period at the end of the previous sentence for those who wish to change the laws of mathematics and the universe to suit their own agenda.
edited to add,..... please forgive my singular view to this judgment asked for and received,... I meant ill will towards no one,.....