If you are still being billed you definitely still have any active premium account somewhere, so its worth checking all of your possible log in details (Spotify username and through Facebook).
If you can't find it and would like it cancelled, or want to discuss refunds etc. you will need to get in touch with the customer services team directly using the online contact form and they will be able to assist you further.
If you get an automated email reply back directing you to the community or help pages, you need to reply directly to that email (even if its from no-reply) and one of the customer services agents will get back to you as soon as possible.
The account linked to your community email address has not been charged since August. Therefore, it does look like you have another account. If you could contact the support team on the link given by Peter, they will help you find where your payments are going.
If you include any other email addresses that you may use, that will help them track the account down.