Bmduell Said:
"I have an iCloud with an old email and I want to delete it because my ex is going on the cloud and harassing my current partner. I don’t know the password to the email and was wondering if I could delete the iCloud email or just everything on it."
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Regain Account Access and Secure it:
Perhaps using a new eMail address would be best here. If you think your Apple ID has been hacked, then by all means, it's best to modify your login credentials (Assign a new email address Reset your password), and then setup Two-Factor Authentication and enable it.
In all, I recommend you contact Apple Support, for regaining access to this. They'll run you through the process of updating your iCloud Account's assigned eMail Address.
Apple Contact Info: