Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Is it Teams Essential? If so, this is a commercial license, so you need to manage it via https://admin.microsoft.com > Billing > Your products or Licenses, cancel from there.
The username should be in this format:
user @ bizname.onmicrosoft.com
user and bizname were defined by you when you set it up initially.