Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Is the charge appearing on your bank statement or a credit card? Have you tried contacting your bank/card issuer to cancel the subscription?
If you can't identify the email account the charge is associated with, MS won't be any help.
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In that case you can try asking the bank/card company to reject the charges as fraudulent.
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If they wont' do that, the only remaining option is to close the account that is being billed, and open a new one. Make sure that add a note to NOT transfer this charge to the new account. You have no problem with MS cancelling the service because you are not using it.