Great question. When you sign up for the trial offer - you're only charged when you first start the trial, and you'll be able to access Premium for 3 months - and afterward, you'll pay the regular Premium price.
In your case, when you first sign up for the trial offer - you'll be charged 99p at the start, and you won't be charged again until the 3 months are over.
If you want to avoid getting charged by the end of the 3rd month, I'd recommend checking out this guide on canceling subscriptions.
I hope this helps! Let me know if you have any more questions :)
Billy-JRock Star 17
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