How do I turn off auto-renewal on a subscription?

On Google Play and on a Microsoft account, no: the period you already paid for still runs. Google says that when you cancel a subscription, you'll still be able to use your subscription for the time you've already paid, and gives its own example: buy a one-year subscription on January 1 for $10 and cancel on July 1, and you have access until December 31 and are not charged another yearly $10 the following January 1. Microsoft says you'll still have access to your subscription and all its benefits until it expires, and its answer to "If I turn off recurring billing, will my subscription stop immediately?" is simply No. Neither Apple nor Google's payments profile documentation states a rule either way. What turning the renewal off does not do is get money back: in your Google payments profile, Google says that if you cancel a subscription, any payments you've already made won't be refunded, and that cancellations can't be undone, although you can always re-subscribe.

No. Google is explicit: when you uninstall the app, your subscription won't cancel. Apple's Media Services terms say subscriptions automatically renew until cancelled in the Manage Subscriptions section of your account settings. The renewal only stops when you stop it in the billing rail's own subscription list.

More than a day on Apple and Google Play, and more than two days on Microsoft. Apple's Media Services terms say you will be charged no more than 24 hours prior to the start of the latest subscription period, and Google's Play terms say you may be charged no earlier than 24 hours before the beginning of each billing period; those terms also say you may cancel a subscription at any time before the end of the applicable billing period and that the cancellation applies to the next period. Microsoft is stricter, and lists it as a reason a cancellation fails: cancellations must be more than 2 days before the billing date. Separately from the charge itself, Google says an authorisation hold may be placed on your form of payment up to 48 hours prior to the beginning of the next renewal period, or up to 5 days before it if you are based in India or Brazil. Google's payments profile documentation states no lead time of its own.

Each rail shows it differently. Apple says that if there is no Cancel button, or you see an expiration message in red text, the subscription is already canceled. Microsoft says that if you see Turn on recurring billing instead of a link that says Manage, your subscription is already set to expire on the date shown and you won't be automatically charged after this date. In your Google payments profile, sign in to Subscriptions and select Canceled at the top of the page, where Google lists the subscriptions you have cancelled.

On Google Play, sometimes. Google says some apps let you pause your subscription, that the subscription then pauses at the end of your current billing period, and that the available pause durations range from one week to three months: go to subscriptions on Google Play, select the subscription, tap Manage and then Pause payments, set the time period and tap Confirm. You can resume it any time by selecting Resume on the same subscription. Whether a particular subscription can be paused at all is up to the app, so the documented route for the other three rails is the cancellation above.

Then someone else is billing you, or something is blocking the cancellation. Apple says that if you can't find a receipt from Apple you might have bought the subscription from another company, so check your bank or credit card statement to find out who bills you and cancel with them, and that a subscription received through your wireless carrier or other provider is cancelled by contacting that provider. Microsoft says a Microsoft 365 subscription bought from a third-party retailer such as Amazon, Best Buy or Harvey Norman is managed with that retailer directly, and lists two other blockers worth checking: the payment card used for the subscription may have expired, and if there is money owing you cannot cancel until any overdue amount is paid. Google's fallback in your payments profile is the same idea: if both the Cancel subscription and Manage subscription options are unavailable, cancel through the subscription provider.