The charged me for a DVR Box that I turned in almo...

The charged me for a DVR Box that I turned in almost a year ago. I closed the account out when I moved out of my apt and turned in all of the equipment. Then I go on a deployment and see that my credit score has dropped significantly with a collections charge of 600 dollars. After speaking to the manager and having them retrace when I cancelled service they can find no record of me turning in the DVR box. Lesson of the story KEEP YOUR EQUIPMENT TURN-IN RECEIPT!!! Poor management!!!