Hey @bookssavedmylifepodcast23! Not sure if you've seen this yet, but we have a guide on paid newsletters here65 that includes info on how to see who's currently subscribed, accessing their payment history, etc. (The article is tailored to paid newsletters, but the information is applicable to other types of recurring payment products as well.)
There should be a link included in the customer's receipt emails that allows them to manage their subscription(s), including cancelling them. You can also cancel it on their behalf from their subscriber profile (screenshot included the article).
We don't support payment plans at the moment, but please feel free to file that as a feature request here28! ☺️