NO Error but also no result

Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production

I am trying to change the STATUS of a tablespace using PL/SQL - need to make call in Linux.

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FUNCTION EXT_WEB_ONOFF(XSWITCH IN INTEGER) RETURN VARCHAR2 IS

  RET     VARCHAR2(100);

  CSTAT    VARCHAR2(1);

  XDO     VARCHAR2(2) := TO_CHAR(XSWITCH);

  EXEC_STR  VARCHAR2(100);

BEGIN

  SELECT CASE STATUS WHEN 'ONLINE' THEN '1' WHEN 'READ ONLY' THEN '0' END

   INTO CSTAT

   FROM DBA_TABLESPACES

  WHERE TABLESPACE_NAME = 'EXT_WEB';

  XDO := CSTAT || XDO;

  CASE WHEN (XDO = '01') THEN

      EXEC_STR := 'ALTER TABLESPACE EXT_WEB READ WRITE';

    WHEN (XDO = '10') THEN