You can check to see which payment method you're using to pay for Premium by going to your account overview page here and clicking on the subscription tab.
If you've checked again and there's still no charge from Spotify where you'd expect there to be one, then we suggest you reach out to our Customer Support team here, who will be able to take a closer look at your account and see what's happening.
@Allioz - if you think you've been double-charged, make sure to check out this Spotify Answer, which lists the various reasons this might happen and also what to do about it.
Let us know if either of you have any further questions :)
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