Crear un saldo Inicial dentro de un reporte

Buen dia

veran que necesito crear un reporte de estado de cuenta de cliente credito el cual entregamos al cliente en el cual muestre los credito y debito

el cual ya tengo hecho pero el problema es que he intentado poner el saldo inicial y lo he logrado pero no me esta funcionando bien me

gustaria saber si alguno de ustedes lo ha hecho antes  pego mi query acontinuacion para ver si me pueden ayuda:

select OrderBy, DocType, DocDate, DocNum, CardCode, CardName, Debitamount, CreditAmount, comments

from   (

              select        OrderBy = 0, DocType = 'Saldo Anterior', DocDate = null, DocNum = 0, CardCode, CardName, 

                                  Debitamount = sum( Debitamount - CreditAmount ),

                                  CreditAmount = sum( Debitamount - CreditAmount ),

                                  comments = 'Saldo Anterior'

              from      (

            SELECT  OrderBy = 1, DocType = Case when HInvoice.series = '117' then 'Nota Debito' else 'Factura' end , DocDate, DocNum, CardCode, CardName, Debitamount = DocTotal, CreditAmount = 0, Comments

              FROM   OINV HInvoice

              Union all

              select OrderBy = 1, DocType = 'Nota Credito', DocDate, DocNum, CardCode, CardName,  Debitamount = 0, CreditAmount = DocTotal, Comments

              from orin

              UNION ALL

              SELECT  OrderBy = 1, DocType = 'Recibo', DocDate, DocNum, CardCode, CardName, Debitamount = 0, CreditAmount = DocTotal, Comments

              FROM   ORCT

              WHERE       Canceled = 'N' ) EstadoCuenta

              where  

               docdate between {?Fecha Desde} and {?Fecha Hasta} and

              CardCode = '{?CodigoCliente}'

              group by CardCode, CardName

              union all

              select    OrderBy, DocType, DocDate, DocNum, CardCode, CardName, Debitamount, CreditAmount, comments

              from      (

              SELECT  OrderBy = 1, DocType  = Case when HInvoice.series = '117' then 'Nota Debito' else 'Factura' end , DocDate, DocNum, CardCode, CardName, Debitamount = DocTotal, CreditAmount = 0, Comments

              FROM       OINV HInvoice

             Union all

              select OrderBy = 1, DocType = 'Nota Credito', DocDate, DocNum, CardCode, CardName,  Debitamount = 0, CreditAmount = DocTotal, Comments

              from orin

              UNION ALL

              SELECT  OrderBy = 1, DocType = 'Recibo', DocDate, DocNum, CardCode, CardName, Debitamount = 0, CreditAmount = DocTotal, Comments

              FROM   ORCT

              WHERE       Canceled = 'N') EstadoCuenta

              where  

              DocDate between {?Fecha Desde} and {?Fecha Hasta} and

                            CardCode = '{?CodigoCliente}' ) Movimientos

order by OrderBy, DocDate, DocType, DocNum

El reporte de ve asi

Saludos