lob segment keeps growing although rows are deleted

Hi,

using oracle 11.2.0.4 Standard Edition.

I have a table with several securefile lobs:

SQL> desc civ_visa.MESSAGE_TO_SEND_TO_CENTRAL;

 Nom                                                        NULL ?  Type

 ----------------------------------------------------------------------------------------------------------------- -------- ----------------------------------------------------------------------------

 ID                                                        NOT NULL RAW(16)

 URL                                                        NOT NULL VARCHAR2(2000 CHAR)

 MESSAGE_TYPE                                                        VARCHAR2(200 CHAR)

 HTTP_METHOD                                                        VARCHAR2(100 CHAR)

 REQUEST_DATA                                                        BLOB

 PRIORITY                                                     NOT NULL NUMBER(38)

 RESPONSE                                                          BLOB

 STATUS                                                      NOT NULL VARCHAR2(100 CHAR)

 STATUS_CODE                                                        NUMBER(38)

 LATEST_STATUS_DATE                                                NOT NULL TIMESTAMP(6)

 CONTENT_TYPE                                                        VARCHAR2(200 CHAR)

 ERROR_MSG                                                         VARCHAR2(500 CHAR)

 OPERATOR_NAME                                                       VARCHAR2(50)

 KIT_ID                                                           VARCHAR2(20)

Apps insert rows in table, then rows are transferred rows to another system.

Every day transferred rows are deleted.