If the OP bought a Y fare they wouldn't need to wait for a schedule change to get a refund; they'd just get one. But if the schedule change is unacceptable to you one option provided by the CoC is a refund. The problem is that such a change cannot accurately be predicted and especially on a non-stop flight like the OP is on such a change is rarely enough to reasonably justify a refund. And even if there was such a change and CO agreed to refund the fare paid there is no way to know (or really to expect) that the cheaper fare will be still available at the time.

The OP bought a ticket based on being comfortable with the fare being asked for. Either pay the change fee or let it go, but the difference isn't going to be refunded/credited otherwise. CO doesn't do that.