Hi DeeDee8! Two things to check so we can get this sorted out. Foremost, the charge to your card, has it been posted or is it still a pending transaction? If it's still pending then in all likelihood it was a holding charge placed on your card that will not be withdrawn. If it has been posted, then you will want to take a look at your account overview. If it says you have been subscribed to premium, the renewal date is 30 days out from when you tried to register for the student discount, and the charge will be $4.99 + tax, then despite what was said, you have qualified for the student discount.
Let me know if your situation doesn't fall into either of these situations and I'll help it get sorted, and please don't hesitate to reach out if you have any other questions!