Hello Emily-
I’m sorry to hear about the trouble! I think you were on the right track by trying to re-install the Post and Page Builder Premium plugin.
Generally speaking, you’ll get this error if the plugin’s directory wasn’t deleted correctly when you deleted the plugin. In order to fix it, use your host’s file manager or FTP and delete the directory wp-content/plugins/post-and-page-builder-premium.
Once you’ve deleted the directory, you should be able to re-install the plugin normally. Please let us know if you have any more trouble, we’re happy to help.