Hi Jennie,
To get direct assistance from Microsoft’s billing department, you can contact them through the official support page here: https://support.microsoft.com/contactus. Once signed in with your Microsoft account, select Microsoft 365 and Office, then choose Subscription, account, billing. You’ll be able to chat with a support agent or request a callback.
You can also visit your account dashboard at https://account.microsoft.com to review your subscription and billing details. From there, you’ll also find links to contact support if needed.
Check this link there's a guide on how to get to billing issues. https://free.blessedness.top/en-us/answers/questions/5405158/how-to-contact-billing-department