Thanks guys. Called in (to the German number, as the Dutch number is an expensive toll one) and they were indeed only able to offer LH group flights. There was nothing that really fit well in my schedule so I canceled and rebooked with Transavia out of KLX instead of ATH.
Not great as this means that effectively there are no more flights between ATH<>AMS that fit my schedule properly, but at least for this specific flight things are OK now.