Originally Posted by
Yreal
To me, it seems that the OTA is claiming a part of the refund. They will lose that fight.
Not necessarily. These obscure OTAs try to sell extra add-ons that exempt you from later "administration fees", etc.
If the OP does anything proactive, they would remain subject to whatever was originally agreed with the OTA and the airline. Only if the flight is fully cancelled - and Delta is irrelevant here - then UX would need to refund the OTA who should refund the customer. Only once that hasn't happened properly a credit card chargeback will get anywhere...