How do I cancel a free trial before it charges me?

Three of the four rails document a deadline. Apple says that if you signed up for a free or discounted trial subscription and you don't want to renew it, cancel it at least 24 hours before the trial ends. Google's Play terms say that to avoid being charged, you must cancel before the end of the trial period. Microsoft states its deadline in the part of the Store Terms of Sale that covers third-party subscriptions billed through Microsoft rather than Microsoft's own subscriptions: if you are taking part in any trial-period offer you must cancel the service by the end of the trial period to avoid incurring new charges unless Microsoft notifies you otherwise, and if you do not cancel the service at the end of the trial period you authorise Microsoft to charge your payment method. Google's payments profile documentation sets no trial deadline of its own.

On Google Play, no. That is where a trial differs from a paid subscription: Google's Play terms say that once you cancel your trial, you will immediately lose access to the content and any subscription privileges unless otherwise specified, while for a paid subscription Google says you'll still be able to use your subscription for the time you've already paid. Apple documents no such rule for trials. Its Media Services terms state the general case only: when your subscription to any service or content ends, you lose access to any functionality or content of that service that requires a subscription.

No. Google is explicit about it: 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. Either way the charge is stopped in the billing rail's own subscription list, not by removing the app.

Then you are looking at the wrong account, or someone else is billing you. Google says that if you can't find your subscription, it may be on a different account, and asks you to try switching between accounts. Microsoft asks you to sign in with the Microsoft account you used to purchase your subscription. Apple asks you to search your email for the words "receipt from Apple" or "invoice from Apple" and check which Apple Account was used, and says that if you can't find a receipt from Apple at all, 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. In your Google payments profile the equivalent fallback is Google's own: if both the Cancel subscription and Manage subscription options are unavailable, cancel through the subscription provider.

Check whether it is a charge or a hold. 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, so a real charge can land a day early on both. 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.

Not always, so do not cancel on the assumption that you can. Apple's Media Services terms say that if you start a free trial to a subscription offered by Apple as content provider and cancel before it ends, you cannot reactivate the free trial. Google's Play terms say access to trial periods may be limited to a certain number of trials for each user during a given period, or other restrictions.