SELECT * FROM call_&table_month

call_table_name   := 'CALL_' || table_month;

open o_call_s for 
      'SELECT *
        FROM '|| call_table_name ||' cll ...';

...
v_start_date:=to_date('01.'||v_month||'.'||v_year,'dd.mm.yyyy');
   v_end_date:=add_months(v_start_date,1);
   
   call_table_month  := to_char(v_start_date, 'MM_YYYY');
   call_table_name   := 'CALL_S_' || call_table_month;
...
    open o_call_s for 
      'SELECT ct.CALT_NAME AS CALT_NAME,
             SUM(cll.SUM_MINUTS) AS MINUTS,
             ROUND((SUM(cll.SUM_VOL_IN) + SUM(cll.SUM_VOL_OUT)) / 1048576, 0) AS VOL_MB,
             SUM(cll.SUM_PRICE_$) AS PRICE
        FROM '|| call_table_name ||' cll, 
             CALL_TYPE ct
       WHERE ct.CALT_ID = cll.CALT_ID
         and cll.subs_id = '||to_char(v_subs_id)||'
       GROUP BY cll.SUBS_ID, ct.CALT_NAME
       ORDER BY SUM(cll.SUM_PRICE_$) DESC';
...

select XMLELEMENT(CHARGES,
                      XMLAGG(XMLELEMENT(CHARGE,
                                        XMLELEMENT(CALT_NAME, CALT_NAME),
                                        XMLELEMENT(MINUTS, SUM(cll.SUM_MINUTS)),
                                        XMLELEMENT(VOL_MB, ROUND((SUM(cll.SUM_VOL_IN) + SUM(cll.SUM_VOL_OUT)) / 1048576, 0)))))
      into v_xml
      SELECT ct.CALT_NAME AS CALT_NAME,
            SUM(cll.SUM_MINUTS) AS MINUTS,
            ROUND((SUM(cll.SUM_VOL_IN) + SUM(cll.SUM_VOL_OUT)) / 1048576, 0) AS VOL_MB,
            SUM(cll.SUM_PRICE_$) AS PRICE
        FROM call_table_name cll, 
             CALL_TYPE ct
       WHERE ct.CALT_ID = cll.CALT_ID
         and cll.subs_id = v_subs_id
       GROUP BY cll.SUBS_ID, ct.CALT_NAME
       ORDER BY SUM(cll.SUM_PRICE_$) DESC;*/

select dbms_xmlgen.getxmltype('select * from '||call_table_name) from dual