It might help to share what version of Moodle running and if the account you were using at the time was true super admin and not a admin whose abilities might be restricted from performing plugin removals.
Have you checked error logs of your web service?
Do you have any additional protections set up in web service outside of Moodle?
When you view the plugins overview there are 'All plugins' with the number of and there is a link to
'Additional Plugins' (with a number).
Which are you attempting to remove?
If Additional Plugins, please share it's name.
There are some Additional Plugins that have 'dependencies' ... rely on other plugins.
One should not remove a core plugin ... should just hide those.
'SoS', Ken