Because of all the disruption recently I imagine the back office is currently overloaded, since they have to prioritise by date order. It wouldn't surprise me if it takes a month, and in any case you can't ring up about that until 48 hours to departure - agents have been told not to make enquiries about this since ultimately it would be a zero sum game. But it is perfectly ok to ring up to sort out seats if you can't do so online.