What should I do to show the due balance on the statement when it appears as zero while there is due amount

Let's investigate what's causing the statement to show as zero amount, rima-sharif.

The Balance Due will show a zero amount if your customers fully paid the invoice. Otherwise, the Balance Due will show the remaining amount for the partial payment.

To learn more about recording invoice payments, check out the Record invoice payments in QuickBooks Online (QBO) article. 

Aside from that one, let's make sure we choose the correct date when creating a statement. If you created a Credit Memo, we need to include it in the Date field to show the statements' balance due.

For more details about balance dues on your invoices, refer to this article: Learn more about the balance due on invoices.

I have a link here that provides you with articles about managing your customer transactions: https://quickbooks.intuit.com/learn-support/manage-customers-and-income/misc/02/manage-customers-and-income-global?label=QuickBooks%20Online.

I'm just one post away if you need a hand with running your financial reports or any QBO related. I'm always here to help. Take care always.