If an employee doesn't help you here, contact one of their Billing reps at the phone number on your bill or 1-800-Comcast, chat with them using one of the "Account and Bill" options at https://support.xfinity.com/chat, or visit a Service Center if one is nearby (check locations and hours at http://www.xfinity.com/support/service-center-locations/) and have them reverse the charge.
In addition to getting the billing corrected, consider setting up a Purchase Pin on each of your cable boxes/DVRs to prevent this from happening. See https://www.xfinity.com/support/articles/how-to-block-purchase-of-pay-per-view and/or https://www.xfinity.com/support/articles/x1-parental-controls-turn-puchase-protection-on-off.
I would like to look into this for you from here. To protect the privacy of your account, can you provide your full name, street address including city, state, and zip code (and apartment number if one is associated), and the full account number or phone number associated with your services. To send a private message click on my name, then click private message me.