Your Neon plan automatically renews each calendar month. If you don't want your plan to renew, you can cancel your plan in 'My Account'. Choose 'Plan & Payment' and under 'Manage your plan', click 'Cancel'.
If using a mobile device, you will need to use the menu (top left) to access the 'Plan & Payment' option. Don't worry, you can reactivate your plan again at any time by logging back into your account and clicking resume.