Cannot edit- Time to move on

Invested a lot in what I thought was an integrity-filled graphic designer. They knew I only wanted the project completed and then I would be doing editing on my site.

I have since found it hard to edit. Now I have had a designer inform me that this “designer” used many plug ins and other things that have hid many pages and makes it very hard for me to edit.

Where to from here?

I hate cornerstone so that is not an option however I am worried about moving to a theme and losing access.

As a non develper and wanting to keep wordpress.org what should be my best step? Would a new theme solve my abiltiy to edit content and add in blocks ect, pages.

Any insight would be appreciated.