I customised my statement to show description, description/memo but it does not show up.

I see what you mean, Amtec. 

When you customize your invoice, it's important to save the customizations as a template so you can continue to use this template moving forward. The first thing to do is check to see if you're selecting the correct template when you create your invoice. You can see a list of templates you've created by clicking the Gear icon > Custom Form Styles. If you don't see your invoice template in the list, that means you likely edited one of your invoices, and didn't save the template. 

If you do see your invoice template here, take note of what you've called it and select it when you create your invoice by clicking Invoices > New Invoice > Customize (at the bottom of the screen) > select your template. 

Take a look at this article for more information regarding your invoice template customization options: Customize your invoices, estimates, and sales receipts in QuickBooks Online. This article has step-by-step instructions for how to create and design your template. 

I hope this helps get you back on the right track. Let me know if there's anything else I can do to help. 

Cheers!