The debt resulted by the student loan is treated differently from other debts - it is almost never discharged in bankruptcy procedure and as in your situation it may be offset by tax return or some other payments. In additional, student loans do not have a statute of limitations.
Generally - as your wage garnishment started - you are not able to stop it unless the debt is paid off. Since your student loan got into "default" status the full balance of the loan is due immediately and other options for delaying payment can no longer be used.
Some states have the law that prohibited wage garnishments or at least limit garnishment by only high paid persons. But that will not eliminate your debt.
As your loan had an interest - the debt will increase as long as you have an outstanding balance - so there is nothing surprising your debt is more than doubled over years even you paid some amounts.
The common way to reduce the interest is to refinance the student loan. You may get low introductory rate and use that time to reduce the principal.
Please be aware that there are some programs that allow to discharge the student loan debt - http://studentaid.ed.gov/PORTALSWebApp/students/english/discharges.jsp While not many could be eligible - it is possible to have your student loan debt discharged (canceled) or reduced, but only under certain specific circumstances.
Government agencies will not provide refinancing for you - you need to contact commercial lenders and compare rates from different lenders. Please be aware that each lender has different qualification requirements for refinancing - so be sure to verify if you qualify.
Student loan rates vary by lender and by your credit history - before filing application - get your credit report and take care to fix problems if possible. Rates for refinancing federal student loans change once a year - normally on July 1. As currently the rates are very low - it is a good time for refinancing.
If lower rates are not an option - you may look for extending the duration of your loan - that might reduce the financial pressure .