If a plugin has broken your site and you can't reach wp-admin, you can turn it off from cPanel.
WordPress Toolkit
- In cPanel, open WordPress Management.
- Select the site and open the Plugins tab.
- Switch off the plugin you want to deactivate (or tick several and click Deactivate).
File Manager
- Go to wp-content/plugins.
- Rename the plugin's folder, for example from
contact-formtocontact-form-off. WordPress deactivates it automatically. - To deactivate all plugins, rename the plugins folder itself to plugins-off, then create a new empty plugins folder.
Once you can log in again, reactivate plugins one at a time to find the one causing the problem. Rename folders back before reactivating.