Getting Due Accounts

I’m really having a hard time in getting the due accounts of a certain customer in MS Access. I have three tables - customerinfo, bills, payments. In my bills tables, a certain customer already had three bills and the customer only made a single payment. The total cost of the bills is worth 1500.00 whereas, in the payment the customer only pay 500.00. If I make use of the SUM function in my query I’ll get a sum of 1500 from payment table.

SELECT, customerinfo.firstname, customerinfo.middlename, customerinfo.lastname, Sum(bills.amount) AS SumOfamount, Sum(payment.amount) AS SumOfamount1
FROM (customerinfo INNER JOIN bills ON = bills.custid) INNER JOIN payment ON bills.custid = payment.custid
GROUP BY, customerinfo.firstname, customerinfo.middlename, customerinfo.lastname;

You should not join the bills and payment tables

       (select sum(amount)
          from bills
         where = bills.custid) as SumOfamount, 
       (select sum(amount)
           from payment
         where = payment.custid) as SumOfamount1
  from customerinfo

Thank you so much swampBoogie.