Broken lease on credit three years old

I am trying to buy a house and when they checked my credit they found a broken lease. I got transferred three years ago not before completing my lease. I have a broken lease on my credit report from that apt complex. I always paid my rent on time and did not break the lease. It's weird how this just showed up on my credit now. I called them apts and they now have all new staff and would not even speak to me and asked that I call the collection agency. What do I do? I did not break the lease I left the place clean.