Originally Posted by Adam Smith

The website doesn't always work properly. It's possible that, for some reason, even though you were entitled to a full cash refund, it was offering you something other than what it should have.

It might be worth consulting your original booking confirmation and checking the fare rules. If those confirm it was fully refundable with no fees, you can either call in and have a reservations agent process a full refund to your card, or write in to refund services and have them process it.