Oracle Temporary table Space reasons for excessive use and sizing In Oracle how to find which operations/queries are causing excessive use of Temporary table Space and how to estimate its size?
you can use this query to find whats exactly is filling temp tablespace

SELECT a.username, a.SID, a.serial#, a.osuser, b.TABLESPACE, b.blocks,
c.sql_text
FROM v$session a, v$tempseg_usage b, v$sqlarea c
WHERE a.saddr = b.session_addr
AND c.address = a.sql_address
AND c.hash_value = a.sql_hash_value
ORDER BY b.TABLESPACE, b.blocks;