Skytree tower tickets for Mon 30th March

I'm looking to buy tickets to enter the Skytree Tower. Ideally both decks, but just the 350 m deck will do if we can't get tickets to the 450m deck. We're going on Monday the 30th of March, and we already have a reservation for the Sky Restaurant.

Last time I went to the Skytree Tower I had no issue buying the tickets the night before. But now I'm having a look on the website and it's showing absolutely nothing available for Monday. It's not even showing sold out, I just physically can't click the Monday, see
here.

Am I missing a trick? I now realise that there is likely to be higher demand that day, because it looks like the prices are going up from the 1st of April. Surely the tickets would not already have sold out – or am I too late?

Thanks.