how to contact customer service?

I'm afraid that contributors here in Q&A do not have access to your account or billing info. We are your fellow users of Microsoft products and services.

Verify in your account at https://account.microsoft.com/services that the subscription was successfully canceled. Typically, you need to turn off recurring billing before you can cancel (see https://support.microsoft.com/en-us/accounts-billing/subscriptions/cancel-a-microsoft-365-subscription).

Not all subscriptions can be canceled, and not all cancellations will result in a refund. For more information, have a look at https://support.microsoft.com/accounts-billing/subscriptions/how-to-get-a-refund-on-a-microsoft-subscription .

If something goes wrong and you need assistance from Microsoft support, start with the chat support at https://support.microsoft.com/contactus .