If they don't match you've got a problem. Does the email address that shows up under Settings->System->About match the email address you used to log in at https://my.roku.com ? Also, don't confuse the serial number with the Device ID.
In addition to what @renojim mentioned, if you need further assistance with account related issues, please reach out to our support team directly here for your 'Account or billing' issue, here: https://support.roku.com/contactus. They will be able to further assist you.