Free Account mailbox limit of 5 - We have 3. So what is wrong?

Free Account mailbox limit of 5 - We have 3. So what is wrong?

I am using Zoho Mail free account which allots 5 mailbox users. Interestingly enough I had 7 mailboxes. I would imagine these wer  grandfathered under free account. Anyway, I erased 4 yesterday. So now I am at 3 mailboxes and everytime I try to add a 4th mailbox (whih still should be free) I get the following notice.
 
  "Max user license limit reached. Please purchase/ugrade license to add more user(s) with mailboxes."
 
Clearly I should be allowed to have up to 5.
 
Can anyone tell me what is going on?
 
Thanks,
 
James