The fact that an itinerary is available on the ANA site is not in itself conclusive as availability can vary from programme to programme. For the same reason, phoning the operating airline directly is not helpful either, as reservation agents will more often than not have no clue as to what has been made available to DC.
What you could do, though, is try to build the itinerary segment by segment (LED-VIE and VIE-LHR) to check availability on each segment, as this sometimes work even where the system tells the DC agent that there is no through availability.