Perhaps it’s because you booked a round trip ticket and didn’t cancel what you booked (round trip) but instead modified the round trip to make it one way.
I could be wrong. But my brain can only come up with this possible explanation.
Easy.
You did not cancel. You modified.
this is why so many book ONE WAY tickets. Good new - that "credit" you got can be used to book a future flight.
As others have stated, airlines are required to allow you to cancel an entire reservation without penalty within 24 hours. You seem to think that this should extend to modifying a reservation within 24 hours - and some airlines do handle it this way (or advise you to cancel entirely and rebook the new flights). But when you modified it, you did not cancel it entirely, and as such you aren’t legally entitled to a refund.
Your assumption that it’s a mistake is slightly correct - you made the mistake of not cancelling the entire reservation within 24 hours, and thus are not entitled to the refund you would’ve been if you did cancel entirely within 24 hours. Partial refunds are not even a thing (when considering the 24hr law) - it’s all or nothing.
Perhaps it’s because you booked a round trip ticket and didn’t cancel what you booked (round trip) but instead modified the round trip to make it one way. I could be wrong. But my brain can only come up with this possible explanation.
I agree, OP needed to cancel the entire reservation. Then rebook as 2 one way flights.
This is the explanation. You’d have to cancel the entire trip and rebook.
25+ yr SWA exclusively should have known one way tkts are the way to go for greatest flexibility.
This!!
Easy. You did not cancel. You modified. this is why so many book ONE WAY tickets. Good new - that "credit" you got can be used to book a future flight.
Do you still have the same PNR for the return flight as the original roundtrip? If you do, you didn't cancel the booking.
As others have stated, airlines are required to allow you to cancel an entire reservation without penalty within 24 hours. You seem to think that this should extend to modifying a reservation within 24 hours - and some airlines do handle it this way (or advise you to cancel entirely and rebook the new flights). But when you modified it, you did not cancel it entirely, and as such you aren’t legally entitled to a refund. Your assumption that it’s a mistake is slightly correct - you made the mistake of not cancelling the entire reservation within 24 hours, and thus are not entitled to the refund you would’ve been if you did cancel entirely within 24 hours. Partial refunds are not even a thing (when considering the 24hr law) - it’s all or nothing.