[GENERAL] Function doesn't work properly

[Ing . Eris J . Gómez]

Hi all. 

I wrote a function and it does not work properly. What am I doing wrong?
*- Here is the script .

---
CREATE OR REPLACE FUNCTION "public"."cxp_balfactura" (x_codcia char, x_suplidor 
char, x_factura char, x_monto numeric, x_moneda integer) RETURNS numeric AS
$body$
DECLARE
       cursor1  record;
       debitos  numeric(14,2);
       creditos numeric(14,2);
       balance  numeric (14,2);
BEGIN
       balance := x_monto;

--It doesn't execute this lines, why?

       for cursor1 in select 
cxp_mov_item.tipo_transaccion,sum(item_monto+item_descuento) AS monto
               from  cxp_mov_item,cxp_mov_head
               where cxp_mov_item.cia_codigo = cxp_mov_head.cia_codigo
               and   cxp_mov_item.mov_codigo = cxp_mov_head.mov_codigo
               and   cxp_mov_item.fact_codigo = x_factura
               and   cxp_mov_head.cia_codigo = x_codcia
               and   cxp_mov_head.supl_codigo = x_suplidor
               and   cxp_mov_head.id_moneda = x_moneda
               and   cxp_mov_head.mov_estado <> '*'
               GROUP by cxp_mov_item.tipo_transaccion
      loop
          if cursor1.tipo_transaccion = 'ND' then
              debitos := debitos + cursor1.monto;
          end if;

          if cursor1.tipo_transaccion = 'CK' then
              creditos := creditos + cursor1.monto;
          end if;

          if cursor1.tipo_transaccion = 'NC' then
              creditos := creditos + cursor1.monto;
          end if;
      end loop;

      if balance is null then
         balance:=0;
      end if;

      if creditos is null then
         creditos := 0;
      end if;

      if debitos is null then
          debitos := 0;
      end if;

      balance := balance + creditos - debitos;

      update cxp_facturas set fact_balance = balance
      where cia_codigo = x_codcia
      and fact_tipo = substr(x_factura,1,2)
      and fact_codigo = substr(x_factura,3)
      and supl_codigo = x_suplidor;

return balance;
END;
$body$
LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;
-- 

Thanks in advance.