MX Already Exists

Hi everyone, I activated my start 10M and email account to try the service. Some days after, I bought a Personal Hosting, I deleted my start 10M plan and email associated to it, but these are still on my account, so when I try to activate an email account on my "Personal" host, the error is "Order not possible. A MX for [domain] already exists" (where [domain] is my domain xxx.it).

How can I fix this? I really need some email accounts on my host.

Thanks to who can help me.
Best regards.
Andrea.