Language Fuel has a client portal that you can log into, to manage your subscription. This includes changing credit card details, and also cancelling the subscription. 


When you first sign up for a membership, you will be given access to your client portal.


The URL is here:

https://subscriptions.zoho.com/portal/languagefuel/login


If you have forgotten your username and/or password, you can re-set it by clicking on the "Forgot Password?" link.