It is a different flight and a different flight number. It's also a commuter airline instead of a mainline jet. But the agent interpreted this as a schedule change and refused to refund it. She said I could take my chances and ask for a refund through the web, which will take two weeks to process.
I was also under the impression that a passenger was entitled to a refund whenever there is a change of operating carrier (as in your case) but I cannot find any reference to that. Maybe another FTer can chime in.