To stop the billing on your old Azure account, you will need to contact Azure support. Since you no longer have access to the old account, you will need to provide the support team with the necessary information to locate and close the account. You can create a support request for this issue.
It's important to note that if you have exceeded the free credit amount on your old account, you will be charged pay-as-you-go rates for any services you're using. To avoid getting charged, keep your usage within the limits of free services.
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