Hello,
Could you please confirm whether you purchased the Microsoft 365 subscription from a Windows or Android device, or through an app store on an iOS or Mac device? If you purchased it through an Apple app store, it is possible that you used an Apple ID that ends with @icloud.com. In that case, you would need to manage your subscription using that Apple account.
You may need to check the order history for that Apple ID to see whether the subscription was made there.