How can we improve WHMCS?

The problem we are facing is that when a client overpay on an invoice. For example the invoice amount is $200 and the client pays $250. The $50 credits sits under his account to be applied to the next invoice.

The issue comes in is that overtime the credit applied to invoices throw out the customer statement and results in the actual amount owed to us and the amount shown on the invoice is not the same.

Can any credits on the client account also show on their statement so that the amounts owing and the balance on the statement is the same.