That's generally only the case for domestic fares. International fares are totally different.

You must read (and PDF!) the fare rules prior to purchase, otherwise you have to trust what CO tells you...and they're not always right the first time! Of course this is difficult when purchasing a ticket over the phone, but fortunately Continental.com lets you request mileage upgrades and will process them if available.

That being said, here's my guess as to what might have happened. Generally whenever you make a change to a ticket prior to starting your journey, the ticket is completely re-priced at the current fare, subject to the rules of that fare. Like purchasing a new ticket. This is usually outlined in the Penalties section of the fare rules of the ticket. So when the OP changed the ticket the first time, it was then re-issued as a B fare with different rules -- specifically a $250 change fee. Fares and fare rules change all the time so it would not surprise me that a $1766 Bxxxx fare was refundable a month ago but a $1766 Byyyy fare has a $250 change fee today.

Assuming this is what happened -- you still have a "claim" because the agent should not have rebooked a refundable ticket as a nonrefundable ticket. It's possible the new refundable B fare was more expensive when the rebooking took place, but the agent should have notified the customer of this.

I'd elevate to a supervisor, who should be able to review the PNR history and see the old and exchanged ticket numbers. But of course you risk learning that the first agent incorrectly waived the change fee...