Are you on the Desktop Advantage auto renew plan?
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-subscriptio...
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.