Payment Arrangement not made as requested

At the end of last year I made a Payment Arrangement with MFC regarding my Car. I had recently been dismissed from my job and had explained the situation to them. as requested by them I sent through all the documentation they required. Today, to my surprise, I had a phone call from a collections agency saying that I had been handed over. according to them no arrangements had been made and I need to pay the money by 12h00 tomorrow. no I have a ruined credit record thanks to some one not doing their job!