Accessing, sharing, and managing documents and media within Microsoft Teams Free
Hello
If you have a paid Teams account, it can mean this is a Teams business account, not a personal Microsoft account.
When you signed up for the business plan, it would have you create a new username that ends with onmicrosoft.com. The subscription will be managed via this link https://admin.microsoft.com with the onmicrosoft.com account credentials. Once you sign in, find Billing > Licenses to locate this paid subscription, and to cancel it from there.