返回第三方网站后网站是否返回发布数据

I am building Recharge Website. So I am collecting information from the user like Mobile No./Operator/Amount. and when the user clicks on Pay button then website goes to Payment Gateway website (3rd Party website). and gives me success/fail response, If the status is success then I want the Users Post variables to form API call to other websites.

I am Storing Users information in Session by this code:

  if(isset($_POST['submit'])){
    $_SESSION['number'] = $_POST['number'];
    $_SESSION['option'] = $_POST['option'];
    $_SESSION['amount'] = $_POST['amount'];
  }

and return this data in Success URL like

<?php echo $_SESSION['number'];>

but. website does't shows the values.

so any other way to return variables after returning website from 3rd party website.