can't access email

Hi,

I set up Zoho mail for an acquaintance a while ago. As of today, he can't access his email all of a sudden. If I do a password reset the password reset link is sent to the address we don't have access to any more.
There is only one user, which is the super-user, which is de account we don't have access to.
How can we get a password reset? It is important to get it asap as it is a bussiness and he can't access all new bussiness email.
Thanks!