They didn't specifically mention a service fee with the refund, because they didn't actually inform me of how they calculated what they refunded. It was clear by the amount given per ticket that it was handled as a voluntary cancellation, as you say.

I checked on Saudi as you suggest, it is marked REFUND. I've no reference to know if this was recently changed.

I don't recall a signature being required at the airport, to be honest I thought it was such a simple process based on previous experience that I'd have the refund processed in a few days. Lesson learnt on that one!

Thanks for your input.