If you have canceled your subscription but you are still receiving bills, then you have one or more additional accounts with Grammarly. You may have mistyped your email address and unintentionally created a new account.
To find the account that's charging your card, please search every mailbox that you use for the word "Grammarly" to find any of our emails. Once you find the right email address, you can reset your password and log in to the account to cancel the subscription.
If this doesn't help, then please visit this page to find your paid account.