ORA-03297: file contains used data beyond requested RESIZE value

Dear Experts,

I want to shrink table space NBG_DATA.

I have moved all objects from NBG_DATA to other tablespace.

Now NBG_DATA seems empty.

select count(*) from dba_extents a where a.tablespace_name='NBG_DATA';

 COUNT(*)

----------

        0

First i'm trying to check free spaces of all datafiles that belongs to NBG_DATA. it seems OK.

Then im trying to shink each data file. but getting error as belows.

alter database datafile 137 resize 500M;

alter database datafile 137 resize 500M

Error report -

ORA-03297: file contains used data beyond requested RESIZE value

03297. 00000 - "file contains used data beyond requested RESIZE value"