How do I dispute a charge off from rental company?

[scottfam4]

My husband and I bought a house in 2003. We talked to the property management company about getting out of our lease early. They told us that we would be charged three months rent for breaking the lease, but if the apartment was rented out before three months, we would only be charged for the time it was empty. We were moving out, and the couple who lived upstairs told us that they were going to be moving into our old apartment. A week later, I went to pick up our mail, and the apartment was occupied. Four months later we received a letter from a lawyer saying that we owed $1800 for breaking the lease. I wrote a letter back explaining the situation and never heard anything about it again. This year, we applied for a home equity loan and were denied. We got our credit report and there was an $1800 charge off as bad debt entry from the property management company. I disputed the validity, and the property management company validated it. I called and spoke with them, and they told me a new lease wasn't signed until July 23rd - almost three months to the day from when we left. I told her that there were people living there a week after we moved out, and she said then they were living there illegally. I'm kind of at a loss as to what I should do about this. If I pay the $1800 will that fix my credit? I don't know the name of the tenants who moved in, and I don't have a copy of the letter I sent to the lawyer in September 2003. Help.