Please see the following concerning Grammarly's payment policy:

Continuous Service Membership: To ensure uninterrupted service, all subscriptions to Grammarly are renewed automatically, using the credit card on file. All of our subscriptions are renewed at the current subscription rate when the current subscription term ends. You may cancel at any time.  

If you have been charged by mistake or there has been an error in billing, please submit a support ticket detailing the issue.  A support representative will review your case and assist you with your refund request. If you do not hear back from us in a timely manner, please check your email's Spam folder -- many email providers block unrecognized email addresses to protect you from Spam and other email scam attempts.