My Navient account was over charged

My Navient account was over charged in the amount of $497. As soon as I realized the error I immediately contacted Sallie Mae. They said I would be reimbursed within the week. One week later I still had not be refunded my money. I called again. After being transferred several times and hung up on once I was eventually assured that my money would be returned to my account by the end of the week ending in 12/7/12. When my money had still not been refunded to my account I filed an e-complaint on the company’s website. After 48 hours i received an email stating that LESS THAN HALF the total amount due to me would be returned within 30-45 days. I find this absolutely unacceptable and an abhorrent business practice.