a co-signer on a student loan

I am a co-signer on a student loan that was defaulted by the borrower. On 11-26-2012 I made the final payment on the loan and over paid by $17.63. I talked with their customer service on 12-23-12, 01-04-13, 01-11-13 and all reps Barbara, Sjs, and Brian (respectively) all told me 7-10 days, the checks in the mail. Also e-mailed on 01-21-13, twice and to this date I have not heard from the company. Anytime I was late with a payment, a forebarance amount was added and late fees were added. My last phone call to them was a 45-60 minute wait period. This company has some problems. Can you help on my situation. thank you in advance.