Did Amazon previously charge you $99 for Amazon Prime? Then the $49.50 may be the 50% off discount you get for being a student.

It never happened to me but you should try calling Amazon or email them about the issue. If it showed up in your bank account you can call the bank, but if it showed up in your Amazon.com user account then it may be an issue with the Amazon company.

Nice.

wonders if this will magically happen for you hehhee