You can cancel at any time, this is not a contract.
If this is the case, you have logged into two different accounts as your account is shared between the app and website. An easy way to confirm this is head to your account area on the app and look at your email address and then head to your account area on the website and look at your email address. If they do not match, you have created two accounts. This often happens if you have already created an account with username/email and password and then you login with Apple or Facebook and your Apple or Facebook email address does not match your JSA account email address.
The Pay-as-you-go Plan is a free plan which all users are switched to after their trial or after their paid membership ends. It allows you to access your programs for free and to request new ones for a small fee.