How can I fight this?

My Property Management sent a one time special assessment bill for $101.34 in Dec'07 to the wrong address (property no belonging to me) even though I have provided them with my correct address on 3 seperate occassion prior to that date. Being that I had no idea I had to pay this bill, due to not receiving the paper work, it went unpaid. Six months later I received a collection request from an Attorney for $304.36. I contacted the my property management office whom confirmed that the information was sent to wrong location and advised that they would have the attorney office cancel all collection attempts including extra fees (Interest, Administrative fee, Attorney's Fees etc). They requested that I send the original paymentof $101.34 directly to them which I did on June 5, 2008. The problem is that they still have not cashed my check. I sent a dispute letter to the attorney on June 24, 2008 to protect myself. Now, the Attorney sent me a written verification with the property management stating that I still owe this money including all added fees, even though I was told directly the opposite from the property management office. I even have a voice mail on my cell on June 20 from the property management office stating that they took care of everything, I have nothing to worry about, stating that they even sent an e-mail directly to the attorney requesting immediate cancellation of collection attempts. Now I have 15 days to pay the $304.36 before more fees are adding on. I truly should not have to "pay" for an error that the property management office made. Only if they had sent the bill to the correct address it would have been paid back in Dec'07. How can I fight this? Can I report the property management to a higher authority?