@aneczka That's your answer, right there. Pre-pay account refunds are not actioned by BACS but by cheque because there's no way of knowing exactly who is due the refund, even if your name is account holder. They'll send a cheque so that the account holder retains the responsibility of giving the refund to the appropriate person.
@aneczka Not so, I'm afraid. The way Scottish Power look at it is that anyone's prepayment card can be charged up by anyone, so unused credit belongs to the person who dipped their hand in their pocket, not the person who is responsible for the meter.
Why not call them and authorise them to send the cheque to a friend still in this country who can pay it into your bank account for you... banks don't insist payees make cheque deposits.