Unable to store data to a local XML file

I have the following code which I'm trying to use to save and load data from a settings XML file on my phone (the caller is accessed via an interface in a PCL)

// caller

public void SetStringValue(string name, string val)
    {
        UserData.SetPropertyValue(this, name, val);
    }

// userdata file

namespace PreferencesXML.iOS
{
public static class UserData
{
    public static object GetPropertyValue(object data, string propertyName)
    {
        return data.GetType().GetProperties().SingleOrDefault(pi => pi.Name == propertyName).GetValue(data, null);
    }

    public static void SetPropertyValue<T>(object data, string propertyName, T value)
    {
        data.GetType().GetProperties().SingleOrDefault(pi => pi.Name == propertyName).SetValue(data, value);
    }

    private static string pUserSettingsFile;

    private static UserSetting userSetting;

    public static UserSetting UserSetting
    {
        get
        {
            if (userSetting == null)
            {
                if (File.Exists(UserSettingsFile))
                {
                    userSetting = Serialiser.XmlDeserializeObject<UserSetting>(UserSettingsFile);
                }
                else
                {
                    userSetting = new UserSetting();
                    Serialiser.XmlSerializeObject(userSetting, UserSettingsFile);
                }
            }

            return userSetting;
        }

        set
        {
            if (value == null)
            {
                throw new ArgumentNullException("value is null!");
            }
            // end if

            userSetting = value;
            if (File.Exists(UserSettingsFile))
            {
                File.Delete(UserSettingsFile);
            }

            Serialiser.XmlSerializeObject(userSetting, UserSettingsFile);
        }
    }

    public static string UserSettingsFile
    {
        get
        {
            if (string.IsNullOrEmpty(pUserSettingsFile))
            {
                pUserSettingsFile = Path.Combine(AppDelegate.Self.ContentDirectory, "UserSettings.xml");
            }

            return pUserSettingsFile;
        }
    }

    public static string Company
    {
        get
        {
            return UserSetting.companyName;
        }

        set
        {
            UserSetting settings = UserSetting;
            settings.companyName = value;
            UserSetting = settings;
        }
    }

    public static double Pi
    {
        get
        {
            return UserSetting.pi;
        }

        set
        {
            UserSetting settings = UserSetting;
            settings.pi = value;
            UserSetting = settings;
        }
    }

    public static bool OnOff
    {
        get
        {
            return UserSetting.onOff;
        }

        set
        {
            UserSetting settings = UserSetting;
            settings.onOff = value;
            UserSetting = settings;
        }
    }
}

public class UserSetting
{
    public string companyName{ get; set; }

    public double pi{ get; set; }

    public bool onOff{ get; set; }
}
}

As you can see, it's not doing anything mind boggling difficult. The reader part of this works fine, but the SetPropertyValue constantly returns a fail at the SingleOrDefault.

This is down to the caller extension method extending the class the caller is in rather than the UserData class.

As the UserData class is static, I can't create an object instance of it and pass that in in place of the this parameter, neither can I pass UserData in directly or as a generic parameter (such as this.SetPropertyValue<UserData>(...)). I've attempted to make the class non-static, which gets me a bit further, but not much.

Is there a way that I can use this code to store data to and from my UserData class?