Can I erase all my company's data and start all over again or cancel the existing one and create another with the same name?

I've got you, @accounting-viafe.

It's my pleasure to present the whole process of how to start over with a clean slate in Quickbooks Online (QBO). 

Yes, you can erase your QBO account if it's less than 90 days. Please note that you're unable to restore or reverse them.

Do the following: 

1. Log in to your QBO account. 
2. Change the URL https://app.qbo.intuit.com/app/homepage to https://app.qbo.intuit.com/app/purgecompany.

        3. The summary of the items to be deleted will pop up.

        4. Type the word YES once the data gets deleted, then click OK.

        5. Hit Wipe Data.

But, if it's 90 days old or older, I'd suggest cancelling your account. Then create another company file with the same name. To do this, perform the following actions:

1. Sign in to QBO as an admin user.
2. Go to the Gear icon, then select Account and Settings.
3. Choose the Billing and subscription tab.
4. In the QuickBooks section, pick Cancel subscription.
5. If you use payroll, you should cancel your payroll account too.

Complete these steps to get a new account:

1. Go to https://quickbooks.intuit.com/choose-country/.
2. Fill up the User ID and password.
3. You can use the same user ID and a password you previously had. 
4. Follow the on-screen instructions. 

You also have an option to export some of your lists into Excel. So, you can import them easily to the brand-new company. For more details: Move your lists to QuickBooks Online.

Moreover, browse through these articles below to learn about the life of QBO after cancelling the account and other billing information:

• Account management
• What happens to my QuickBooks Online data after I cancel?

Please let us know in the comments if you have any additional questions in handling your account or other concerns. I'm always here to help you. Be safe.

@accounting-viafe 

If you are using QBO Simple Start, you should cancel your account and open a new blank one instead.

https://quickbooks.grsm.io/EU