Zoho Bonus User Signup Error

Zoho Bonus User Signup Error

 I received an invitation to join Zoho. I will need the offered bonus users to create enough mailboxes for my business.
I did not use the email address I received the invitation to set up the account and aparently that is what creates the link to claim the bonus mailboxes. I have not yet set a new MX record because I need to be certain I can add the addtional 5 boxes once I have moved to ZOho. Will that oppurtunity appear nce I change my MX record?
 I have submitted a support request but so far have received no answer.
Is there a way for me to claim the mailboxes that were offered?
I have tried to change my primary email to the correct one. When I do a box comes up that says that the email address already exists and will not allow me to use it as one of my email addresses.
Any suggestions??
 
Mark