Hi Nathan.
I'm sorry, your situation is unfortunate. It's difficult to stop a garnishment already in action without filing bankruptcy, but it can be done. Basically, all you can do at this point, since the deductions have already begun, is talk to the creditor and explain what happened. Sometimes they will be willing to drop the writ and accept payments from you. HOWEVER..The garnishment only lasts 90 days, and it really may be in your best interest to allow the garnishment to continue, since the max garnishment on a student loan is 15%, and any payment arrangement the creditor would accept would be higher than that. Also, the black mark is already on your credit report, there is nothing you can do about that.
I'm sorry about this situation, it really does suck. If you need help or have any questions, I work in payroll/HR and would be glad to help. Good luck.