Accidental rental

My soon to be 3 year old got a hold of the remote and accidentally rented a movie. Is there a way to cancel the rental?

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 the 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.