Refund to customer paying through Revolut declined

[AlexMcGann]

Issued a refund to a customer of our e-commerce business who mistakenly ordered the wrong item through our Shopify store.

The refund showed up on their Revolut account, only to say "Declined", apparently without giving them the option to accept the refund.

They are now asking for the refund to be issued again, although there is no option to do so as it says it's already been deducted from next months payout. 

Is there any way I can resolve this?