Why am I being charged for Heroku Scheduler?
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.