some has set up a Microsoft 360 email account using a domain that does not belong to them. How do I cancel the account?

Hello Dr_Agan,

Good morning!   

Thank you for publishing in Microsoft Community. We are happy to help you.   

Based on the description you have shared; we understand that some users from your tenant (organization) have set up a Microsoft 360 account using a domain that does not belong to them.

It's important to know the type of account you're using, because each account has a different process and a different support category.  

What type of account is affected? is outlook.com account, Hotmail account, or professional/educational account.  

Typically, if your organization is business account to cancel a Microsoft 365 email account that was set up using a domain that does not belong to the account holder, you will need to take the following steps:

1. Sign in to the Microsoft 365 admin center using your admin credentials.

2. Go to the Users > Active users page.

3. Find the user account that you want to delete and select it.

4. Click on the Delete user button.

5. Follow the prompts to confirm the deletion of the user account.

However, if you mean that an organization (Microsoft 360 email account) is using domain that does not belong to them.

First note that in O365 organization (tenant) if any domain has been added somewhere else (tenant), you can't add that domain in your organization(tenant), If you have bought any domain with a provider, trying to add in O365 organization (tenant) and notice that an organization(tenant) is using the domain.

You need to double check with your domain provider first and if you have all proof that you are the owner, kindly create Microsoft support ticket to contact our Data protection with all detail about your domain to help you.

 please see below for instructions:  

1. Create a Service Request in the O365 Admin Portal and indicate the request as clearly as possible. 

2. Or you can contact our hotline and we will create a Service Request ticket for you Global Customer Service phone numbers (microsoft.com)   

You can try during the phone call, press "1" as business email user, and then press "1" again as technical support. You also need to provide information purchased from your subscription, such as company name, phone number, etc.  

Please feel free to let us know if there are any questions or if we got you wrong. We will continue to assist you based on the information you provide. We sincerely appreciate your patience and cooperation. 

Sincerely   

Eben Ezer Tres | Microsoft Community Moderator