[Tex/LaTex] Special format for chapter title

Question

I want to format my chapter title for example:

"Chapter one: Introduction"

I have a new command defined as the following:

\documentclass[a4paper,12pt] {report}
\usepackage{thesis_packages}

\newcommand{\ch}[2]{ 
\setcounter{chapter}{#1}
\setcounter{section}{0}
\chapter*{#2}}

\begin{document}

\include{introduction}
\end{document}


% introduction.tex
\ch{1}{Chapter One: Introduction}   \label{ch:intro}

For that, I need to write \ch{1}{Chapter One:intro} in the introduction.tex file. However,I receive an error says "undefined control sequence \ch{1}{Chapter One:intro}".
The new command is defined in the main text file. I use report documentclass.

Answer 1

\documentclass[a4paper,12pt]{report}

\makeatletter
\newcommand{\inletters}[1]{\ifcase \csname c@#1\endcsname
  zero\or one\or two\or three\or four\or five\or six\or seven\or
  eight\or nine\or ten %complete here if you have more than 10 chapters 
  \else ??\fi} 

\renewcommand{\@makechapterhead}[1]{\vspace*{50\p@}%
  {\parindent\z@ \raggedright \normalfont\Huge\bfseries
    \ifnum \c@secnumdepth>\m@ne \@chapapp~\inletters{chapter}: \fi
     #1\par\nobreak\vskip 40\p@}}

\def\@chapter[#1]#2{\ifnum \c@secnumdepth >\m@ne
    \refstepcounter{chapter}%
    \typeout{\@chapapp\space\thechapter.}%
    \addcontentsline{toc}{chapter}%
    {\@chapapp~\inletters{chapter}: #1}% <-- modification
  \else
    \addcontentsline{toc}{chapter}{#1}%
  \fi
  \chaptermark{#1}%
  \addtocontents{lof}{\protect\addvspace{10\p@}}%
  \addtocontents{lot}{\protect\addvspace{10\p@}}%
  \if@twocolumn
    \@topnewpage[\@makechapterhead{#2}]%
  \else
    \@makechapterhead{#2}%
    \@afterheading
  \fi}
\makeatother


\begin{document}

\chapter{Introduction}

In this chapter, ...

\section{First section}

\end{document}