The problem is that your class declaration does not fit the XML format...
What your code is expecting is a group of League nodes enclosed in a League node to form a kind of array:
<XMLSOCCER.COM>
<Leauge>
<Leauge>
...
</Leauge>
<Leauge>
...
</Leauge>
</Leauge>
...
</XMLSOCCER.COM>
Now, you can change the structure of your XML to fit the declarations or change the declarations to fit the XML...
XML changes
<XMLSOCCER.COM>
<League>
<League>
<Id>1</Id>
<Name>English Premier League</Name>
<Country>England</Country>
<Historical_Data>Yes</Historical_Data>
<Fixtures>Yes</Fixtures>
<Livescore>Yes</Livescore>
<NumberOfMatches>5700</NumberOfMatches>
<LatestMatch>2015-05-24T16:00:00+00:00</LatestMatch>
</League>
...
</League>
...
</XMLSOCCER.COM>
Code changes
[Serializable()]
[XmlRoot(ElementName = "XMLSOCCER.COM", Namespace = "")]
public class XMLSOCCER
{
[XmlElement("Leauge")]
public Leauge[] Leauges { get; set; }
[XmlElement(ElementName = "AccountInformation")]
public string AccountInformation { get; set; }
}