high i/o consuming sql statement

[Papik]

We are executing a billing process and after do the report with tkprof, we have found a very consuming i/o process. We have moved the table and rebuild the indexes but it appears being i/o consuming.
This is the tkprof result with the statement:

UPDATE LOG_FACTU SET SERIAL_FACTURA=:b1,CODIGO=:b2,DATOS=SUBSTR:b3,1,100)
WHERE
ID_PROCESO = :b4 AND PRC_ID_CORRIDA = :b5 AND ID_CLIENTE = :b6 AND
ID_LINEA = :b7

call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 0 0.00 0.00 0 0 0 0
Execute 24839 26768.35 29886.37 3591776 78521078 248400 24839
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 24839 26768.35 29886.37 3591776 78521078 248400 24839

Misses in library cache during parse: 0
Misses in library cache during execute: 1
Optimizer goal: CHOOSE
Parsing user id: 20 (FACTU) (recursive depth: 1)

Rows Execution Plan
------- ---------------------------------------------------
0 UPDATE STATEMENT GOAL: CHOOSE
0 UPDATE OF 'LOG_FACTU'
0 INDEX GOAL: ANALYZED (UNIQUE SCAN) OF 'XPKLOG_FACTU' (UNIQUE)


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We didn't find the cause of this, any ideas or suggestions what to look for ?
Thank you very much