Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
First, please feel free to check out the AI answer
Since the monthly subscription appears to be linked to an old address that you can no longer access, you may not be able to cancel it yourself. This is a public forum, so no one here can view the account, stop the payment, or issue a refund.
Please contact Microsoft Support, enter "live chat". You will be prompted with an option "Ask out Support Assistant". Kindly click on it and type in "I need live chat agent to support my billing questions" - choose Contact Support and select Microsoft 365 and Office - Billing and Account profiles questions to request help from the billing team. Have the charge dates, amounts, payment-card type, and last four digits available, but do not post those details publicly
You can also use Manage your payments and select Investigate. This may help locate another account using the same card.
Thank you for your understanding and time