I cannot add more than three users

I cannot add more than three users

Hi, I have just upgraded my organization space with a premium version; I have already paid for annual account.
Now my space is upgraded to 10 Gb.
I have 3 users, previously invited during the trial version; now, despite upgrading, I cannot invite other users!

Moreover, I would like to know the maximum number of users I could invite to my premium docs area.

Please, help me as soon as possible.
         
Thank you in advance