Nelnet Student Loan Complaint

Nelnet Student loan department,

Federal student loan servicing Dealing with my lender or servicer Trouble with how payments are handled California

Nelnet has combined my subsidized and unsubsidized student loans without permission. I used to have a Group A and Group B student loan that I paid to them. Now - -I have only a Group A. I intend on going back to school next year - -so, I intend on only paying the unsubsizided since the interest will still accrue. They have done so without my permission. I have tried to call multiple times - -and have gotten no resolve. I am on time AND ahead - -but I have every right to pay either loan in advance by law. How many times are they going to manipulate my loans?