Go to your settings page and scroll down to the section called 'your subscription'. Here you can cancel your current subscription.
(Note that you need to be logged in to see this page).
You can cancel the subscription at anytime and you will still have access to the period you have already paid for.
If you do not have an active subscription then you have another account, perhaps one with Google or Facebook login that you have recently changed email on.
Step by step Guide:
1. Click your profile picture
2. Scroll down and click "Edit your profile"
3. Scroll down and click "Cancel subscription"