I got spotify premium a month ago with the first month free deal with the payment method where it goes onto my next phone bill, I was charged £10 straight away after subscribing and cancelled but I am still getting charged on my phone bill.
If you're paying through your mobile provider, it's them who cancel the service, since it's them who charge you for it in the first place.
Your Spotify account gets linked to your mobile number and that's it. No payment info is recorded in Spotify's systems, and therefore no charges can be made.
You need to go and talk to someone from your mobile provider and ask them to stop the service.
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