Recently, I have faced this issue, a plugin folder named “themify” was not being deleted from all the options a normal user have.
Tried all above options, including wordpress plugin managed to delete it, but I they reappear every time I do. The folders get deleted on file manager of cpanel but when I refresh page they reappear, on FTP it says cannot delete files.
I want to delete everything uploaded on the server in order to upload a fresh plugin to get things worked.
Nothing worked, until I came to know, that this plugin folder was created by root by his own ftp account. Thats why i was unable to delete it. So, i must have root access and its user logged in via ssh or ftp to get deleted this kind of issue.