You probably have PHP errors that you are not seeing, try adding these lines to the top of your php:
error_reporting(E_ALL);
ini_set('display_errors', true);
This code will enable error reporting, which probably will make you see something..
Also, this line:
if($_POST['Duvidas'] = "Outras Dúvidas")
is not comparing $_POST['Duvidas']
with "Outras Dúvidas"
but is assigning the value "Outras Dúvidas"
to $_POST['Duvidas']
, which is always true.. Use if($_POST['Duvidas'] == "Outras Dúvidas")
instead (note the ==). This might be cause of your problems.