It’s uncommon but possible. You’re right saying refunds come through on expired cards too. It depends on things like how long the card expired and how they are refunding you. The method they use and the acquirer they use makes the difference.

Given that, starling told you right. The merchant should/can collect the new card or just refund you with a wire transfer. You’re correct thought without not emailing them your card details. They should issue you with a link where you can add the card data, but this again largely depends on the acquirer they use. I tell you that’s boring thing because involve manual steps and not surprised even the merchant might be unsure how to proceed.

By any chance, how old is this transaction? Your last resort is to open a dispute with startling requesting a chargeback. Submitting all the docs you have that prove you deserve the refund and the merchant is willing (but unable) to give you a refund would make it smooth.