You don't mention in your question how you produced the string instead of the number. You mustn't redefine \thechapter
, or all references pertaining to the first chapter will have the string ONE
.
You can patch the \@makechapterhead
instead, with the following:
\documentclass{report}
\usepackage{fmtcount} % for textual representation of numbers
% patch \@makechapterhead
\usepackage{etoolbox}
\makeatletter
\patchcmd{\@makechapterhead}
{\thechapter}
{\NUMBERstring{chapter}}
{}{}
\makeatother
\begin{document}
\listoffigures
\chapter{First}
\begin{figure}
A
\caption{A figure}
\end{figure}
\end{document}

If you want to have “CHAPTER ONE” in front of your chapter title in the table of contents, you need to patch also \@chapter
.
\documentclass{report}
\usepackage{tocloft}
\renewcommand{\cftchappresnum}{CHAPTER\ }
\setlength{\cftchapnumwidth}{10em}
\usepackage{fmtcount} % for textual representation of numbers
% patch \@makechapterhead and \@chapter
\usepackage{etoolbox}
\makeatletter
\patchcmd{\@makechapterhead}
{\thechapter}
{\NUMBERstring{chapter}}
{}{}
\patchcmd{\@chapter}
{\protect\numberline{\thechapter}}
{\protect\numberline{\protect\NUMBERstringnum{\arabic{chapter}}}}
{}{}
\makeatother
\begin{document}
\tableofcontents
\listoffigures
\chapter{First}
\begin{figure}
A
\caption{A figure}
\end{figure}
\end{document}

Note that you need \cleardoublepage
before \listoffigures
, if you want it in a new page. For showing the output I did not add it.