HTMLEditor can take a bit of time to uninstall, I have seen it take an hour in some instances, there are many files that need to removed, and the Extension manager will remove the files one at a time. One thing that can add to the time it takes to uninstall HTML Editor is having many files stored in the systems trash or recycle bin.
If you give it some time, HTML editor will uninstall.
If you would rather pursue a refund, please contact the sales department at sales[at]webassist.com