There are two things that could have happened here:
You hit the button twice when upgrading. If this is the case the two charges will be on the same date and your next payment date will be 2 months away. You can check by visiting your subscription page here.
You’ve created a second account and subscribed to that one too. Are the charges on different dates? Check your other email inboxes for emails from Spotify--that can give you a clue as to where the second account is registered. You can then cancel the second account by following the steps here.
If you still want to get in touch with our Support team, we recommend that you contact us here or through our official social media channels on Facebook or Twitter. This way, we'll be able to take a closer look at your account and see what happened there.
Let us know how it goes and if you have any other questions.