Hey there, Nguyen
If you have accidently upgraded your subscription, please reach out to the Azure Billing team through the Azure portal here: https://portal.azure.com
Once you have signed into your account, please click onto Help + support on the bottom of the left-hand side navigation menu.
Please create a new support request
This will allow you to complete a support request so you can contact the Billing team. Hopefully it will allow you to contact the billing team at Azure.
Thanks,
Nathan