The discounted rate will automatically begin on your next billing date. Anyway, if you think you're eligible to get a refund, I suggest you get in touch with the Spotify staff - simply drop them a line on social media (Twitter or Facebook) or by using the contact form. Make sure, if you use the latter, to reply to the automated email you'll receive directing you back to the help pages, even if it's from a no-reply.
Support usually gets back within a day or two.
By the way, in which country are you?
BittencourtRock Star 21
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