Same file looks different when opened in Acrobat vs Illustrator

[ARCcolor]

We created a pdf in Illustrator using links.  However, after updating and saving the file with a new linked image, the pdf still opens in Acrobat Pro with the old link.  We've tried saving as different file types other than pdf, and deleting the image and relinking the new one again.  No matter what we've done, the file still opens with the old linked image.  Is there anything we can do to save this file instead of starting over?

[Monika Gause]

So you are definitely replacing the old file? You are sure that you are opening the new one in Acrobat?

What happens if you don't overwrite the old one, but save it witha different name?