Email already exists

Hello! I am trying to add a user/email to our custom domain with zoho: thenatureschool(dot)org(dot)au. I added jodinka(at)gmail.(dot)com and she registered with Zoho as per the link. I then went to control panel and as the super administrator tried to create her email: jodie(at)thenatureschool(dot)org(dot)au but it keeps saying that it already exists...but it doesn't?! I had no issues with the other account I created in the same way. I have already written to your support email some days ago but haven't received a reply. Can you please help me?! Thank you, Lloyd