Welcome to the Spotify Community. Sorry to hear you're being double charged!
We recommend you check out this page and go through the steps. Since you mention you've been paying double, make sure to read through the 'Paying more than once a month' section. These steps should definitely help you out.
It would also be good to check out this article on how to find the possible second account. Let us know how you get on, we're here to help 🙂
Have a great day.