Can't join GAC

Since last week I'm unable to join Grand Arena, I have 2 acc so I assumed I missed the join green button in both of them. But today after receiving every season reward (with a hard drop form kyber 4 to aur 5) I find myself unable to join again, in both acc.
Has anyone else got the same problem?? What day of the week exactly are you supposed to join GAC? Any help will be awesome!