I believe that refunds by bank transfer are only available within the consolidated EU banking system (although this clearly violates the EU regulations on train delays). I think that there are two options you might consider:

• Get a voucher for your next trip on DB Bahn (which will be mailed to you via snail-mail - if they refuse to send it to you, insist or complain to the "Schlichtungsstelle Fahrgastrechte": https://soep-online.de/ [unfortunately, german only])
• If you happen to be in Europe in the next few weeks, hand in the form (as long as the conductor placed a stamp on it) at a DB Reisezentrum (ticket office) and you should have no trouble to be refunded in cash