Try to change this line
<cellStyles count="1"> <cellStyle name="Normal" xfId="0" builtinId="0"/> </cellStyles>to
<cellStyles count="1"> <cellStyle name="Normal" xfId="1" builtinId="0"/> </cellStyles>but I am not an expert on the xlsx xmls... Try to take time and study with excel app (and unzipping xlsx) what the underlying xmls actually represent.