Any time that you enroll in a class at a college or university, there is a set deadline for class withdrawals. If you withdrew in time (e.g. before the deadline), and you did not receive a refund, you may qualify for an unpaid refund cancellation.
Please note that, in the case of federal student loans, the refund may have been provided directly to the lender. This should be reflected on your statement of account with your lender.