Alias EmailID already exists

Alias EmailID already exists

Hi. I now have my new Zoho account set up as <firstname>@zoho.com, with <firstname>@<mydomain> as an alias and as default email.

I need also to have <firstname>.<secondname>@<mydomain> configured as an alias, but when I try to add it I get a message that: "Alias EmailID already exists".

I've seen some previous (quite old!) threads suggesting that previously configured aliases can get "stuck" in your database for 30 days. Is this the problem here? Can someone resolve this so that I can add the additional alias please? 

I would prefer not to post the full details of my addresses in public forum...