space reclaim with xmltype

I am having trouble in getting back the space for the table PAYLOAD

CREATE TABLE XXTIBCOFRAMEWORK.PAYLOAD

(

    PAYLOAD_ID NUMBER  NOT NULL,

    LOG_ID     NUMBER      NULL,

    DATA       XMLTYPE     NULL,

    CONSTRAINT PK_PAYLOAD

    PRIMARY KEY (PAYLOAD_ID)

        USING INDEX TABLESPACE XXTIBCOFRAMEWORK_TS

                    PCTFREE 10

                    INITRANS 2

                    MAXTRANS 255

                    STORAGE(BUFFER_POOL DEFAULT)

    ENABLE

    VALIDATE

)

The above table is heavily used around  3 million record is being inserted every day .

We have a purge script which deletes 21 days old data but not seeing the space back .

select owner, segment_name, segment_type tablespace_name, bytes/1024/1024/1024 gb from dba_segments

order by gb desc

    

OWNER

SEGMENT_NAME