Magento 2 Success.phtml output order values - magento

Question

We're having some issues with Magento 2 where we're unable to output the order values in our checkout code. Here's our code:
<!---- Onefeed Tracking Code ---->
<?php
//-------------------------------------------
// GET MAGENTO ORDER VALUES FOR TRACKING CODE
//-------------------------------------------
$orderId = $block->escapeHtml($block->getOrderId());
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$order = $objectManager->create('Magento\Sales\Model\Order')->load($orderId);
$total = $order->getGrandTotal();
?>
<script type="text/javascript" language="javascript">
var of_ssid = 'xxxx';
var cs = '<?php echo $total ?>';
var oi = '<?php echo $orderId; ?>';
var it = 1;
</script>
<script type="text/javascript" language="javascript" src="https://tracking.onefeed.co.uk/t.js"></script>
<noscript>
<img border="0" src="https://tracking.onefeed.co.uk/ProcessProductCheckout.ashx?of_ssid=xxxx&cs=<?php echo $total ?>&it=1&oi=<?php echo $orderId; ?>" />
</noscript>
<!---- End Onefeed Tracking Code ---->
Any ideas how we can output the data without having to create a module in Magento 2?

Answer 1

This part of your code is definately working (just checked):
<?php
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$order = $objectManager->create('Magento\Sales\Model\Order')->load($orderId);
$total = $order->getGrandTotal();
?>
...
<?php echo $total ?>
Since I don't know which Block functions you are relying on it's impossible to say for sure, but I'm guessing $orderId = $block->escapeHtml($block->getOrderId()); does not return a valid order id.
I'm not sure if you should use objectManager though. There is quite a discussion about when and how to use it on the stackexchange:
https://magento.stackexchange.com/questions/117098/magento-2-to-use-or-not-to-use-the-objectmanager-directly