Unable to mock a static property of a single ton class

Question

ObjectData which contains the singleton property:

public class ObjectData
{
    public static IObjectData singleTon 
    {
        get 
        {
            // code for singleton
            return new ObjectData();
        }
    }

    public virtual T CreateObject<t>()
    {
         return //single object of T ;
    }
}

Singleton helper which sends a type for creating an object:

public static class SingletonHelper 
{
    public static Model myModel
    {
        get { return ObjectData.singleTon.CreateObject<Model>(); }
    }

   
} 

     // Model which contain a property of folderName
   

     public class Model {
       public string folderName {get;set;}
    }

    // pathCalculate for which I am going to write unit test
   public class pathCalculate {
        public string myFolderName 
        {
          get { return SingletonHelper.myModel.folderName }
        }

   }
    
// I have tried 

// Assign
Mock<IObjectData> objectData = new Mock<IObjectData>();
Mock<Model> model = new Mock<Model>();
model.Setup(m => m.folderName).Returns("my expected folder Name");
objectData.Setup(m => m.CreateObject<Model>()).Returns(model.Object);

//Act
pathCalculate cl = new pathCalculate();

//Assert
Assert.AreEqual("my expected folder Name", cl.myFolderName);

In the Assert part, I get an error

myFolderName** value Null

I believe using this code there is some problem while mocking the CreateObject function.