I can help you cancel your QuickBooks Online (QBO) account by going to the Billing & Subscription page. Once the account was canceled, your data will be available in read-only access.
Here's how:
Go to the Gear icon.
Under Your Company, select Account and settings.
Click the Billing & Subscription tab.
Select Cancel subscription.
Click Continue to cancel.
Follow the next steps provided on the screen.
Click Submit and cancel subscription.
Select Got-it.
I'm including these articles for more information regarding canceling your account: