Duplicate records Entity Framework 6 (generic update)

Question

I made a similar example Many-To-Many Generic Update Method with Entity Framework 6 1

But in my case, the values of the properties of the collection are re-created in database.

 public void Update(T updateItem, string property)
    {
        using (var databaseContext = new TelesystemContext())
        {

            T foundDal = databaseContext.Set<T>().Find(updateItem.Id);
            var entry = databaseContext.Entry(foundDal);
            entry.CurrentValues.SetValues(updateItem);

            var collection = entry.Collection(property);
            collection.Load();
            collection.CurrentValue = typeof(T).GetProperty(property).GetValue(updateItem);


            databaseContext.SaveChanges();
        }
    }

The property is re-created when is saved updateItem, instead of adding to the table - a bunch of "many-to-many".