Help Save me From Drowning

Earlier in September, I had to make use of a rental car for a period of two days.  Despite careful care with the car, they decided to charge me $300 for cleaning related to smoking, despite the fact that no one smoked in the car, and neither I, my partner, nor his father smelled anything at the time of returning it. 

They overdrew my account by changing the initial charge, which not only took away money I was counting on, but also earned additional bank penalties. The cascading problems from this have been making my situation exponentially worse, essentially eating all the money I had left and then some.  I'm still waiting to hear back from the company after contacting them and them promising to investigate. 

I'm panicking and I don't know what to do. I don't get my next disability payment till the end of the month and have another bill due before then. I have less than no money until then. I'm doing my best to try and earn some extra money, but that likely won't come till the end of the month either. 

I just want to go back to some semblance of stability.  Any little bit helps in helping to make me not be completely sunk by the rental companies unfair dealings.