Well, the title says it was a mistake booking through Expedia. I stand by this.
When trying the book the exact same ticket directly with the airline (+5%) later on, the ticket was issued straight away and the money was deducted from the debit card. The only trouble is that I am out of EUR 8200 (Expedia failed booking EUR 4000 + airline direct booking EUR 4200); Expedia told me that the refund/release may happen after 30 days. And yes, for that I feel "wronged" by Expedia.
I was using a debit card, because it offers close to 0% foreign exchange fees. The credit card wants 1.75%. When talking about a ticket value EUR 4000, that's the reason why the debit card was used.
Moreover, I was able to claim Air Berlin-related chargebacks through that debit card before.