What can I do about a Rent Debt, if anything at all?

My mom and I moved into an apartment complex around March of '08 and we had a one-year lease we ended up leaving in october of '09 because my dad had came back from south america for some personal issues. we gave the apartment complex a 2 month notice and heard nothing back, then we sent a reminder notice a month later and they said they were never notified be we moved out anyways because we had proof of the first letter we sent. I had turned 18, before moving in, when we left the apartments I was 19, I hadn't had a job at all while living there, they sent me and my mom a bil for about $4,000 then a few months later it sky-rocketed to $6,000. most of the charges were replacing the carpet in the apartment, but what I don't get is that they were remodeling all the apartments anyway, we saw them change everything, the doors, new paint, new carpet, new trims, they charged us for not cleaning a laundry room which was dirty and dusty when it was handed over to us in the first place, the bulk of it was for the carpets though. The first bill was $4,000 and that included in there and then the next had an added $2,000 added to it, which wasn't explained at all it was just there. It shows on my mom's and my credit report, how can I be liable I only signed that I was a resident living with her but they made it clear that what I was signing wouldn't hold me liable if the cirstance ever came up. My credit report says "This account is scheduled to continue on record until Jul 2015." I've tried to contact the apartment complex but none of the people that were there when I stayed there, are still working there, nobody wants to help or cares to because I have been hung up on and have never had calls returned. I don't want to wait that long, what can I do?