You upgraded from Simple Start/Simple Start to Essentials, or from Essentials to Plus mid-billing cycle.
You have multiple companies, which means you will be billed for each one.
You forgot to cancel a subscription (cancelation has to be done manually by the master admin user).
You saw a second charge related to the pre-authorization process for credit card payments:
If you are checking your credit card account online, please be aware that QuickBooks submits a pre-authorization before processing your subscription payment. This pre-authorization allows us to verify that the credit card on file is valid and that there is enough available credit to process the charge. Typically the pre-authorization is removed within five days.
If your payment was very recent, you may still see the pre-authorization on your account. Intuit's pre-authorizations can be up to $0.50 more than the actual charge, so if the amount is not what you thought you were being charged for your subscription, this could be why. Additionally, since the pre-authorization is temporary, you may see the charge online, but will not see this on your credit card statement.
If you have any questions, you can verify the pre-authorization by calling your credit card company.