If your loan servicer is not working with you to solve issues, such as discrepancies with your loan balance, you can file a formal complaint. You can contact the CFPB online here or call 855-411-2372. The CFPB will work with the loan servicer on your behalf to solve the problem.
After exhausting your other options, you can also contact the student loan ombudsman to help reach a resolution. A student loan ombudsman is a neutral third-party who will work with you and your servicer to identify the problem and a solution.