How do I cancel my bill on Apple Account

You will need to provide a little more information on what you want to cancel. If you have a subscription that you no longer want, you can cancel that here:

If you want to cancel a subscription from Apple - Apple Support

If you are looking for a refund for a purchase you made, then you can try to make a refund request. All transactions in the App Store are final, but on occasion Apple may provide a compassionate refund. It should never be expected though.

Request a refund for apps or content that you bought from Apple - Apple Support