Hello
If you go to https://account.live.com > Services, do you see two plans, one annual and one monthly?
If you do, make sure you cancel one of them.
For further billing support and refund, go to https://support.microsoft.com/contactus, Type "Billing" and press Enter. On the next screen, click "Contact support" at the bottom of the page, then choose "Microsoft 365" > "Manage my subscription". You’ll then see the option to chat with a Microsoft support agent who has access to your account to help review the issue.