Issue
You have provisioned the free Heroku Scheduler but are seeing charges for it on your invoice.
Resolution
These charges stem from scheduler Dyno usage. The Heroku Scheduler add-on is $0/month, however, it's an add-on that is used to spin up a Dyno, and 1X dynos are $0.05/hour. In the add-on page, you can find this information under "Dyno-hour costs" in the Documentation.
To stop further charges, you can use Heroku Dashboard to either switch your app to Free Dynos or delete the Scheduler add-on altogether.