Thanks! It has been resolved. Apparently my FileZilla didn't show hidden files on remote server, that's why I can't see .htaccess that was still lurking.
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QuoteInternal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, firstname.lastname@example.org and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.