My categories got hidden….pls help

All my existing posts have been uncategorized. When I go to the Category in admin panel, I cannot see any of the category I originally had. I tried adding them again, but I get the error message

“The category you are trying to create already exists.”

If it is there then why can’t I see them.

Is there a way I can get the category showing again and how do I link each post to its category ?

The issue is similar with Category links. It is not there anymore. But when re-adding it, it adds it successfully. However I cannot see what I’ve added from the Category Links section, and as a result cannot use it to reset my link categories properly.

Appreciate some help on this matter

Thank You