Is it possible to fix this as I have reinstalled the software twice, and I still get the same problem
I think the problem is not at all Photoshop’s.
When you degrade an image by reducing the jpg quality the number of pixels does not change so the uncompressed image (as indicated for the opened file in Photoshop’s Image Size dialog) naturally has the old size.
What are ebay’s image requirements? Do they mention some maximum width/height in pixels?
1.6 million pixels
And which pixel dimensions does your image have?
Be sure you realise that the information shown by "image size", while it is very useful, is NOT the file size and not connected to it.
To get the file size look in Windows Explorer or Mac Finder.
Also, you should use SAVE FOR WEB not SAVE AS, which (a) makes smaller files and (b) previews the actual size and quality for you.