I've had some contact with the ticket agency. I'm in the UK, and sent tickets back about a month ago. Tele Ticket Service say that they are waiting for the concert organisers to refund them another 'batch' of money, then they will refund their next set of ticket holders who have returned tickets.
I am from Holland. Sent my tickets back right after the news of postponement/cancellation. Registered mail, completely filled in form. Got my money back within 3 or 4 weeks.