Kaplan University Over charging Davenport Iowa

I have been attempting to work through the student loans I have with Kaplan University for 2 years. After completing my education, I recieved my student loans that I would be paying back. Which equaled out what was due according to tutition fees. I have now companies calling me stating I still owe over 20K more than what the US Dept of Education state is what the orginal documentation submmitted to them via Kaplan Financial department. 

Now being threaten with garnished wages by a 3rd party collection agency due to being over charged. Not only this they have sent this to three different collection and all agencies are trying to obtained the same amount. 

According to Kaplan University, they are trying to obtain 60K (in total) from me as well as the 60K that was already paid in student loans with the Dept of Education.