What can I do about a problem landlord?

I'm having a problem with my landlords. I moved out of my old apartment because my old landlords were away most of the yr on vacation and it made things difficult for me to get things repaired or handle concerns with the apartment. They frequently needed to come into my dwelling and i had had enough so I moved into another apartment that I later realized was illegal. This landlord is slow to repair things, I have a water leak in my living room as well as an open drain in the floor which I believe I am getting a large amount of my water bugs from. Things in the apartment that were poorly and hastily constructed by the landlord himself tend to fall apart quickly such as towel racks and toothbrush holders and toilet paper hangers. They have insisted that I would not need an air conditioner over the summer due to the coolness of the basement but when I told them it was over 80 degrees in the apartment they shrugged me off as if I didn't know what I was talking about in order to persuade me into not getting an air conditioner. We don't have separate meters and he charges 900 dollars a month for a small one bedroom (the bedroom not much bigger than the size of a california king size bed so its not really a "bedroom") and there is no window in the bedroom. To make things worse, the insulation on the door is terrible and ive had to insulate it myself which wasn't enough and he complains to me if i use an electric heater because he doesn't want to pay the electric for it, yet im freezing down here and he doesn't seem to care" Finally, for six months now i've an infestation of fruit flies that I couldn't kill off. I tried bleach in the drains and fruit fly traps from amazon.com which ran me in excess of 50 dollars and ive had no luck. I noticed they had them upstairs too and so I asked them to call somebody and when I did I was not only shrugged off, but then he proceeds to get aggressive with me and start looking around my apartment for things to complain about and calling me a liar, saying that I use the electric heater all day, and then proceeds to speak in italian swearing up a storm to some stranger ive never met. This goes on and on and on and they've threatened to throw me out over stupid **** before so its time that I find out what my rights are and how I can screw them over in return because they're obviously interested only in my money, and not in being decent landlords, and when I make simple requests im met with hostility and indifference. i don't have the money to move and the rent is costing me half my months salary as it is. Should I go to court and take this matter to a higher level or should I start fighting on my own for what I deserve?