This is not really for the community but for the ones managing Miro, if there is any...
I created the account and has setup my credit card too. 
I want to modify the team size but can not. 
I tried to reach out to Miro team a few times without success. 
I tried to do it via the sales team email too but no answer. 
I had to reduce the budget on my credit card and a result the account will probably be closed. 
I wish there would be a real support team out there.