Have you tried contacting Comair about this. Given they have cancelled the flight, I believe they have the responsibility to you.

In your favour, their Conditions of Carriage for flights they operate (not just ticket) are, surprisingly, more generous than BA's. BA do not commit to rebooking you on another carrier but Comair says you can choose to be re-routed with a different carrier (9. b. 3. "Remedy 2").