I upgrade to Quickbook plus account and paid £12.08 few mins ago, but changed my mind & downgraded back. But was only refunded about £1, my monthly bill increased to £14

It's good to have you here in the Community forum, Frederick. 

When you upgrade or downgrade your QuickBooks Online (QBO) subscription, you may not receive a full refund for the unused portion of the higher-priced plan. To ensure that this problem is resolved effectively, I recommend contacting our QuickBooks Online Support Experts. They will have access to your account details and can assist you in understanding the charges and resolving any billing discrepancies.

Here's how:

1. In your QBO account, click on Help (?).
2. Choose either tab to get started:
   • Assistant: Get quick, personalized answers. Select a suggested option, or type a question or topic you need help with. If you decide you need further help, you can still Talk to a human.
   • Search: Search the QuickBooks Online knowledge base directly, or select Contact Us and choose a way to connect with us:
     • Start a chat with a support expert.
     • Get a callback from the next available expert.

To know our support's availability hours, kindly visit: QuickBooks Online Support.
 

Remember to provide them with all the relevant information, such as the date and time of the upgrade, downgrade, and the amount you were charged. They should be able to assist you further and provide a more accurate explanation of the charges on your account.
 

Moreover, here's an article that consists of short step-by-step videos that will help you with managing your QuickBooks account: Learn about QuickBooks Online with how-to videos.
 

I remain available and prepared to address any inquiries you may have regarding any matters related to QuickBooks. I am always just a comment away, ready to assist you.