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NUS discount is only for one year (may be extended to two years). When your Premium expired due to an card issue, was that after the year of your NUS, or have you had days left?
I think the best thing to do is to get in touch with Spotify, so they can sort this out for you.
You may get in touch with Spotify via their Twitter page (@SpotifyCares), or by following this link to send an e-mail.
If you send an e-mail, please check your inbox (and spam box) to check for their automatic reply. Once you get it, please reply to it immediatly (even if it's from an no-reply e-mail addres) to make sure an Spotify employee will get back to you as soon as possible.