Unable to call using Skype API in C#

Question

I am trying to make calls through Skype API in C#. I can only open Skype but I am not able to make calls. I am looking for some suggestions to solve the issue.

public void MakeCall()
{
    string PhoneName = Mike;
    string MyXMLFilePath = AppDomain.CurrentDomain.BaseDirectory + @"Database\ContactsData.xml";
    XmlDocument MyXmlDoc = new XmlDocument();
    MyXmlDoc.Load(MyXMLFilePath);
    XmlNode RootNode = MyXmlDoc.SelectSingleNode("Users");
    XmlNodeList FirstLevelNodeList = RootNode.ChildNodes;
    foreach (XmlNode Node in FirstLevelNodeList)
    {
        XmlNode SecondLevelNode1 = Node.FirstChild;
        if (SecondLevelNode1.InnerText == PhoneName)
        {
            XmlNode SecondLevelNode2 = Node.ChildNodes[1];
            PhoneNumber = SecondLevelNode2.InnerText;
        }
    }
    if (PhoneNumber != null)
    {
        call(PhoneNumber);
    }
    else
    {
        MessageBox.Show("Phone number is not available.");
    }
}
public void call(string number)
{
    new WebBrowser().Navigate("skype:" + number + "?call");
}

It's the XML code I use:

<Users>
  <User>
    <Name>Mike</Name>
    <Number>1234</Number>
  </User>
</Users>

Here's the Skype page after I run the code.

Any hint? Thanks in advance.