My LandLord is suing me need advise?

Okay My ex landlord is suing me for $5,000; however i do not owe him that amount he state i owe damage, i must confuse the only damage done to the place was the door. which cost $25 at home depot. and 3 month rent totaling 3,750. the damage should be cover in our security deposit. and plus the reason i moved as i no longer could afford it and i explain my situation. i also no longer had a lease. the apartment needed repair. the celling had fell from a leak he never looked into just cover it and leaked continue to leak. the heater in the apartment was locked by our electrician because the heater was leaking to much C02 that was haz and for two year the landlord never fixed it. the lights switch never had cover on them so it would spark up when you when turn it off sometime causing the fuse to pop. and the hallway light never were on. it was so dark in there. i never complain and when i explain i can not afford this apartment and i was willing to surrounding it,it was okay i don't mind paying him what i owe little by little but i do not owe him $5,000. i need help and advise on what should i do. or what route to go.