I'd be happy to help fix your VAT codes issue, @rgh.
As suggested, you'll want to reclassify all your transactions that were assigned to the wrong VAT code. QuickBooks have a reclassify tool that helps the accountants correct the transactions. Please take note that this option is only available in QuickBooks Online Accountant.
Also, I still suggest contacting our Phone Support Team again. I understand that you've contacted them before, but they're the best support group available to investigate this issue further. And they can create an investigation ticket if other users experiencing the same.
Feel free to leave a reply if you have more questions. I'll be here to answer them for you.