I am not sure how or why this is happening but, I did find something suspect- your print shop dimensions of 36.47" x 46.89" are both exactly 4.168 times bigger than the size of your intended dimensions of 8.25" x 11.25". Curiously, a resolution of 300 is also exactly 4.168 times a resolution of 72.
The designer's document size looks correct in the AI file. Perhaps in the pdf conversion something was changed ? It seems the print shop is expecting a resolution of 72 and the document is actually 300 and therefore they are seeing it 4.168 times larger than intended.
This is a bit of a conjecture on my part but the numbers are saying there is a resolution issue. The whole resolution/dpi/ppi thing is tricky with Illustrator because it is vector and vectors are, by definition, resolution independent- and yet, our monitors and certainly our printers are very affected by different resolutions.