Hello there, @PP17.
I'd like to redirect you to the best support group available to get this addressed right away.
Since it needs to unfile the VAT return to make an adjustment to the figures, I'd recommend contacting our Phone Support Team. This way, they can look into your account in a secure environment and help you unfile the return, then process the adjustment.
To reach them, click the ? Help button at the top right corner and select Contact Us to talk with a live agent.
You might want to check out these articles to learn how to manage your VAT return:
Please touch base with me here for all of your QuickBooks needs, I'm always happy to help. Have a great day and keep safe.