Btukfyl

I am writing my thesis and I face a problem with the appendices.

My code is below:

   documentclass[12pt]{book}



    % package to activate greek language - the sequence languages appear below is IMPORTANT!!!

    usepackage[greek,english]{babel}

    usepackage{varioref}

    %usepackage{hyperref}

    usepackage{float}

    usepackage{multirow}

    % package to handle graphics

    usepackage{graphicx}

    graphicspath{{images/}}

    % package to handle multiple figures in a minipage

    usepackage{subfigure}

    % package to extend math capabilities

    usepackage{amsmath,amssymb,isotope}

    usepackage[version=3]{mhchem}

    %package to activate XeTeX font manager

    usepackage{fontspec}

    usepackage[titletoc]{appendix}



    % DOCUMENT LAYOUT

    usepackage{geometry} 

    geometry{a4paper, textwidth=5.5in, textheight=8.5in, headheight= 15pt, marginparsep=7pt, marginparwidth=.6in}

    %geometry{a4paper}

    setlengthparindent{8mm}

    setlengthparskip{5mm}



    % FONTS

    usepackage{xunicode}

    usepackage{xltxtra}

    usepackage{xcolor}

    defaultfontfeatures{Mapping=tex-text} % converts LaTeX specials (``quotes'' --- dashes etc.) to unicode

    %setromanfont [Ligatures={Common}, BoldFont={GFS Artemisia Bold}, ItalicFont={Gentium Italic}]{Gentium}

    %setmonofont[Scale=0.8]{Monaco} 

    setmainfont{Times New Roman} % You can set your main font here.



    % ---- CUSTOM AMPERSAND

    newcommand{amper}{{fontspec[Scale=.95]{Gentium Italic}selectfontitshape&}}



    % package to handle line spacing

    usepackage{setspace}



    % HEADINGS

    usepackage{sectsty} 

    usepackage[normalem]{ulem} 

    sectionfont{rmfamilymdseriesupshapeLarge}

    subsectionfont{rmfamilybfseriesupshapenormalsize} 

    subsubsectionfont{rmfamilymdseriesupshapenormalsize} 



    % PDF SETUP

    % ---- FILL IN HERE THE DOC TITLE AND AUTHOR

    usepackage[unicode, driverfallback=dvipdfmx, bookmarks, colorlinks, breaklinks, pdftitle={Theo J. Mertzimekis - A thesis template for UoA students},pdfauthor={tmertzi}]{hyperref}  

    hypersetup{linkcolor=blue,citecolor=blue,filecolor=black,urlcolor=blue} 



    % package for fancy style headers and footers

    usepackage{fancybox}





    % redefine bullet symbols and section style

    renewcommandthesection{arabic{section}.}

    renewcommand{labelitemi}{$blacktriangleright$}

    renewcommand{labelitemii}{$bullet$}



    newcommand{itemcheck}{item[checkmark]}

    newcommand{itembullet}{item[$bullet$]}

    newcommand{itemdiamond}{item[$diamond$]}

    newcommand{itemtriangleright}{item[$triangleright$]}

    newcommand{itemcirc}{item[$circ$]}

    newcommand{itemsquare}{item[$square$]}



    % change captions especially for greek language - if the document is in ENGLISH, they should vanish

    addtocaptionsenglish{%

      renewcommandprefacename{Πρόλογος}%

      renewcommandrefname{Αναφορές}%

      renewcommandabstractname{Περίληψη}%

      renewcommandbibname{Βιβλιογραφία}%

      renewcommandchaptername{Κεφάλαιο}%

      renewcommandappendixname{Παράρτημα}%

      renewcommandcontentsname{Περιεχόμενα}%

      renewcommandlistfigurename{Κατάλογος Σχημάτων}%

      renewcommandlisttablename{Κατάλογος Πινάκων}%

      renewcommandindexname{Ευρετήριο}%

      renewcommandfigurename{Σχήμα}%

      renewcommandtablename{Πίνακας}%

      renewcommandpartname{Μέρος}%

      renewcommandenclname{Συνημμένα}%

      renewcommandccname{Κοινοποίηση}%

      renewcommandheadtoname{Προς}%

      renewcommandpagename{Σελίδα}%

      renewcommandseename{βλέπε}%

      renewcommandalsoname{βλέπε επίσης}%

      renewcommandproofname{Απόδειξη}%

      renewcommandglossaryname{Γλωσσάρι}%

      }



    usepackage{xgreek}



    usepackage{csquotes}

    usepackage[backref=true,backend=biber,style=authoryear]{biblatex}

    addbibresource{bibliography.bib}



    usepackage{fancyhdr}

    pagestyle{fancy}

    fancyhf{}

    fancyhead[LE,RO]{leftmark}

    cfoot{thepage}

    renewcommand{chaptermark}[1]{markboth{MakeUppercase{#1}}{}}



    usepackage{afterpage}



    newcommandblankpage{%

        null

        thispagestyle{empty}%

        %addtocounter{page}{-1}%

        newpage}



    %%%%%%%%% END OF PREAMBLE %%%%%%%%%%%%



    begin{document}



    setlanguage{greek} %% this is to activate greek hyphenation

    chapter{Introduction}

    chapter{Related Work}

    ...



    begin{appendices}

        chapter{Μοντέλο}

    end{appendices}

end{document}

The result is:

Does anyone know why this box is appeared next to letter A and how can I remove it?