This is a difficult but not uncommon situation. If you plow through your financial aid paperwork you will find that the contract language specifies that the ultimate responsibility rests with the borrower, the student. You got the benefits from the erroneously refunded money, and those goods and services cannot stand as gifts.
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I'm sorry to hear of the situation you are stuck in, but it sounds like you are, in fact, stuck. The facts you set forth do not appear to support any cause of action against the University. If the charges are legitimate and you agreed to pay them, the mix-up over whether those costs are paid by you separately or directly from the loan is probably your responsibility to correct.
I only practice in Washington State and may not practice in your area. This answer is a brief hopefully helpful tip to you which is correct to the best of my knowledge and is meant as a starting point for you to conduct further investigation. However, it is made without knowing the factual details of your case or doing any legal research and so may be in error as to either the facts or law. I am not your attorney and I am not giving a legal opinion by this answer.