FBCS University of Phoenix Collection Agency Used Loan Paid Off stating they show still oweing full balance Nationwide Nationwide

I recently decided to go back to school to continue my education. I paid off my School Loans in February 2016 or so I thoght. I found out I owed $29.00 still so I immediatly paid that off. I am informed now that I have a ZERO balance and I owe nothing.  Now the University of Phoenix Financial people are telling me that I still owe them. I took two classes that were 5 weeks long and completed those two classes. I did withdraw. I paid almost $4000.00 on those two classes. I have my confirmation number from the Pay OFF in FULL and they are still telling me that I owe them. This FBCS is harrassing me now and wont stop. I have talked to the Manager of the Department of Education and they are stating that they faxed the School the confirmation of Paid in Full on 5/17/2016 which they are stating they  have not received so they faxed it to them again today. University is telling me that they can not call the Department of Education to verify and the Decpartment of Education is telling me that they are lieing to me that they can call them that schools call them every day to get pay off confirmation for students. NOW, this is really urking me in the butt!  I am approved for my financial aid. I have done my requirements and now this is happening. I suggest highly on NOT attending this school. I can not believe that I already am having such troubles with them.