avg_fragmentation_in_percent not changed after Alter Index

I have strange problem
I execute
ALTER INDEX IX_MyTable ON dbo.MyTable REBUILD
---
When i query from sys.dm_db_index_physical_stats
i found  avg_fragmentation_in_percent same not changed
name      table_name      index_id      index_type_desc         avg_fragmentation_in_percent
IX_MyTable       dbo.MyTable      CLUSTERED INDEX                66.6666666666667

I even execute

ALTER INDEX ALL ON  dbo.MyTable
REBUILD WITH (FILLFACTOR = 80, SORT_IN_TEMPDB = ON,
              STATISTICS_NORECOMPUTE = ON);
Nothing happen !!!
What does it means and how to solve this issue to make a de-fragmentation ??

Note: I am  using SQL server 2012