I think what people are telling you is if you have waited till Delta made the change it would have been refundable. The suggestion is you call and tell them now “ after I cancelled, you cancelled so I can get a refund” and that probably won’t work because that’s not the way it works. But I’ll be honest I’m sitting here waiting on one flight booked to change hoping I can get a refund versus a credit. I’ve got another two months, if it doesn’t change I’ll take the credit if it does I’ll get the refund