Why does my vat due read a completely wrong figure - it appears to be recording vat from all invoices in the past year, rather than the last period?

Hello there, nick-dalton.

We have currently open a new investigation about the incorrect VAT due in QuickBooks Online (QBO). Our engineers are closely working on getting this permanently fixed.

In the meantime, we're requesting all users with the same issue to contact our Care Support Team and add your company credentials under the investigation. Below are the steps on how you can reach us out:

1. Click the Help icon in the upper right of the screen.
2. Select Contact US on the pop-up. 
3. Enter what you're needing assistance with in the What can we help with? field and choose Let's talk. 
4. Click Get a callback.
5. Enter your contact information.
6. Select Call me.​

Aside from this, you can also visit this website where service outages or investigation status are provided: http://status.quickbooks.intuit.com/.

Stay in touch for updates or if you have other questions, let me know. I'd be happy to assist.