I'm lost of how flight credits work when you book on AmEx travel. Every time I've cancelled there's no record of my travel credit until they call several departments and find them. The credits also don't show up when I log into my airline accounts.

So I booked a Delta ticket through AmEx travel on 4/28/24 for $1000.70. I wasn't sure if I used that so I called AmEx and after a long call they said the flight credit was still valid but I had to book and travel by 4/28/25. Delta flight credits you only have to book by 1 year from original booking, not travel.
Also I read there's a trick where if you book a ticket on Delta that is more than the credit, then cancel that, they will reissue you a new flight credit with a new expiration date. But I have no idea if that will work in this case because there's no ecredit in Delta so I guess it's an AmEx credit? But another time I canceled an Alaska booking through AmEx and I had to call Alaska directly to use the credit.

Could somebody explain how these credits work? And if there's any way to extend so I can fly this ticket on Delta after 4/28/25?

Thanks!