your select stmt should be some what look like this

SELECT
h.ACCOUNTNUMBER, f.FNAME, f.LNAME, g.JONNUM, h.CIRCUITNUMBER,
g.SERVSTART, g.SERVEND, h.DISCODATE,e.billsep FROM
(SELECT
c.ACCOUNTNUMBER, 
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '10', d.BILLAMT, 
0 ) ) AS BILLOCT,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '11', d.BILLAMT, 
0 ) ) AS BILLNOV,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '12', d.BILLAMT, 
0 ) ) AS BILLDEC,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '01', d.BILLAMT, 
0 ) ) AS BILLJAN,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '02', d.BILLAMT, 
0 ) ) AS BILLFEB,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '03', d.BILLAMT, 
0 ) ) AS BILLMAR,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '04', d.BILLAMT, 
0 ) ) AS BILLAPR,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '05', d.BILLAMT, 
0 ) ) AS BILLMAY,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '06', d.BILLAMT, 
0 ) ) AS BILLJUN,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '07', d.BILLAMT, 
0 ) ) AS BILLJUL,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '08', d.BILLAMT, 
0 ) ) AS BILLAUG,
SUM( DECODE( TO_CHAR( d.INVOICEDATE, 'mm' ), '09', d.BILLAMT, 
0 ) ) AS BILLSEP

FROM
TELCOMUSERS a, ASSIGNMENTS b, SERVICES c, BILLING d
WHERE
a.USERID = b.USERID
AND
b.SERVICEID = c.SERVICEID
AND
b.ASSIGNREFNUM = d.ASSIGNID
AND 
a.USERID = NVL( uNum, a.USERID )
AND
a.DEPTNAME = rDep
AND
a.CODE = rCod
AND
c.SERVICECATEGORY = seCa
AND
c.ACCOUNTNUMBER = NVL( aNum, c.ACCOUNTNUMBER )
AND
c.SERVICETYPE IN ( stBa, stCe, stPa, stCa, stCi )
AND
d.INVOICEDATE >= fDat
AND
d.INVOICEDATE <= tDat
GROUP BY
c.ACCOUNTNUMBER
ORDER BY
a.LNAME) e ,TELCOMUSERS f, ASSIGNMENTS g, SERVICES h
where
e.accountnumber=h.accountnumber and
f.USERID = g.USERID
AND
g.SERVICEID = h.SERVICEID;