my $signed = SOAP::Data->type(string => $XML_CANCELA)->name('cancelacion');
or
my $signed = SOAP::Data->type(string => $XML_CANCELA)->name('cancelacion')->attr({xmlns => 'http://cancelacfd.sat.gob.mx'});

$soap = SOAP::Lite->proxy("${TSERVER}Cancelacion/wsCancelacion.asmx",timeout => 30);
$soap->default_ns($NameSpace);
$soap->on_action(sub {qq¡"${NameSpace}Cancelar"¡});
my $response = $soap->Cancelar(($signed,$tkn));