Did you sign up for free offers for temporary subscriptions to different apps or programs? Are there any services that you need to cancel?
In the future, when you sign up for a trial subscription, immediately set a reminder to cancel it a couple of days before you’ll get automatically charged for it.
If you enjoyed the service and want to keep it, then you’re all set. But, if you realize that you aren’t using the app during the free period then it doesn’t make sense to get charged for it.