Update: IndieGogo has now started refunding the backers. All of a sudden, one morning I received an email that I have been refunded without even officially asking in the recent weeks (last time I asked for a refund was months ago, after that I gave up). Something is still really strange in that whole story, but I feel better now that many backers received their refund. The thing that really worked was a private Facebook group where backers exchanged their experiences. Maybe there's a lesson learned in that as well :)