Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hello, sorry to know about this issue that you have encountered.
As you have an existing subscription, you will need to double check and cancel the duplicate if it is reflecting on the account and then you can go to https://account.microsoft.com/services/microsoft365/billing and try it from there or try to turn off the recurring billing at https://go.microsoft.com/fwlink/?linkid=2277073 and you can also follow the guided steps indicated from the link below which also includes refund eligibility check.
If you will encounter an issue, you can reach out to the support team at https://support.microsoft.com/en-us/contactus/ or use the Get Help app on your PC and then click on Microsoft 365 and then click Get Home Support and then type in Billing question and click the blue button that says Sign in to contact Support and login and proceed from there.