I agree with Darthmoney. The self-help option scans your recent purchases and lists which ones are automatically eligible for a refund but certain products fall outside of that scope.
You’ll want to submit a ticket through the Support site to request a refund for the Skyborne Heroic Edition. they should be able to get that straightened out.
It is strange that you weren’t able to just upgraded from Heroic to Epic. It usually just requires paying the difference.