How do I cancel ALL Turbo Tax accounts including Intuit and Advantage?

You can not delete or merge accounts.

You can try to clear all of the information in your TurboTax account for this year but you will need to Contact Customer Support  to have an account deactivated for more of a resolution.

Intuit - How to delete my account

How do I delete my account? | IRS Free File Program delivered by TurboTax

FOR ADVANTAGE 

You can sign into your Turbo Tax Advantage account and under Your Product, select to Remove Product.  Once you remove the recurring product order, the Turbo Tax Advantage subscription will be cancelled as well.

How to cancel Turbo Tax Advantage

https://ttlc.intuit.com/community/downgrading/help/how-do-i-cancel-my-turbotax-advantage-subscription/00/25548

If you missed the cancelation deadline for this year's TurboTax product, simply wait until you receive your CD or download, then submit an online refund request within 60 days of receiving your product.