I need to stop the billing on my account

If you want to stop billing immediately, you should suspend your account. I assume your account is a stand-alone one, and not part of an AWS Organization, thus you can follow the process documented here: https://docs.aws.amazon.com/accounts/latest/reference/manage-acct-closing.html

This will immediately suspend billing, but also your access to the account. Once you have suspended the account, you can still change your mind, and un-suspend the account for 90 days, however after that it will become permanently closed.

I suggest you change the root-email address on the account to a sacrificial one before you suspend the account, as you can never re-use the root-email address on a new AWS account, should you wish to do so in the future, once the account has been permanently closed.