Not returning uri segments

[eluser]InsiteFX[/eluser]
Yes welcome is the controller name.

Just place the route at the very bottom!

Code:

$route['(.*)'] = 'activate/index/$1';

Thats all you need, you do not need any of the routes you showed!

_remap - Place at the bottom of your contoller.

Code:

// --------------------------------------------------------------------

/**
* _remap()
*
* Remaps the URL segments.
*
* @access private
* @param string
* @param array
* @return mixed
*/
public function _remap($method, $params = array())
{
    if (method_exists($this, $method))
    {
        return call_user_func_array(array($this, $method), $params);
    }

    show_404();
}

Also see this:
CodeIgniter User Guide - Input Class -- $this->input->is_ajax_request()