Called KLM Germany today after changes in my booking. Tried to postpone to August this year which he was willing to do but unfortunately after a couple of mins talking to the back office he was told it is a wrong fare and i could only get a voucher or refund.
Second call to kLM Hungary he mentioned immediately that this is an error fare and however he can only do changes within 30 days. he suggested me to change again and again for 30 days hoping new cancellations would come in. He said also that he spoke to other guys calling with this fare trying to rebook but all of them would refuse after there comes out a huge fare difference.
will try again the next days.