If an employee doesn't help you here in the Forums you'll have to keep trying to contact one of their Billing reps and ask them to issue a credit. Call them at the phone number on your bill or 1-800-Comcast, use one of the options on https://www.xfinity.com/support/contact-us, or visit a Service Center or Xfinity Store if one is nearby and if it is open (check locations and hours at https://www.xfinity.com/support/service-center-locations/).
In addition to getting the billing corrected, consider setting up a Purchase Pin on each of your cable boxes/DVRs and in the Stream app and web portal to prevent this from happening in the future. See https://www.xfinity.com/support/articles/parental-controls-non-x1 and/or https://www.xfinity.com/support/articles/x1-parental-controls-turn-puchase-protection-on-off and/or https://www.xfinity.com/support/articles/x1-manage-tv-settings-online.
The response from Bruce is excellent. I can confirm that the movie was bought from one of your devices, perhaps by someone within your household unbeknowst to you. Highly suggest setting a purchase control/parental control pin to avoid someone mistankenly purchasing content in the future.
With regards to getting refunded. This is quite simple; as suggested, call 1-800-XFINITY and one of our care agents will be more than glad to refund your purchase price.