Welcome to the Community. I'm here to provide information on canceling your account.
Thank you for allowing QuickBooks the opportunity to serve the software needs of your business. @MarshallA has provided the correct steps for canceling a QuickBooks Online account.
Please be aware that your data will be available in read-only access for one year from the cancelation date if you've paid for the software. If this is a trial account, the data will be available in read-only access for 90 days. I recommend the following article for additional insight on cancellation: How to Cancel Your Subscription.
Should you still need the customer service phone number, you can get it with the following steps: