Sending a PDF Vector file for printing (780mm x 780mm) getting cropped out.

Hello everyone!

So, I have sent 3 different files (Big SIze) for printing and one of these is causing lots of problems. I am exporting my work from Illustrator as PDF and sending it to the Printing Shop to be printed as a quite large Plotter (780mm x 780mm) but when the people in the Shop open it on CorelDraw they get a cropped and weird arranged version of my work (Images attached)

The other two files were sent together and were perfectly ok, though they were printed in a different printer (Shop SIgns)

I hope the images I am attaching can provide a more graphic and clear explanation in order to be able to fix it.

Thank you in advance.

Juan Manuel