OP was the text under ticket endorsements like the following? Not sure this means it is really a refundable fare. It seems rather cheap for a refundable fare.
TICKET ENDORSEMENTS
THE ORIGINAL AND THE REISSUED TICKET MUST BE ANNOTATED
- -REFUNDABLE/CXLFEE/CHGFEE - IN THE ENDORSEMENT BOX.
While most assume refundable fares always have no fee to do so, there are sometimes fares that are refundable, but with a fee. From what the OP posted, it sounds like this is one where the value is refunded minus a $300 cancellation fee.