PowerApps is not currently supported here on QnA. I'd try asking for help with billing by creating a ticket here.
https://powerapps.microsoft.com/en-us/support/
or possibly just cancel it out here.
https://account.microsoft.com/services/
--please don't forget to Accept as answer if the reply is helpful--
Regards, Dave Patrick ....
Microsoft Certified Professional
Microsoft MVP [Windows Server] Datacenter Management
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