Invitation Homes review: Maintenance charge

I called into to disclose water backing up in both bathrooms. Mind you, the city came out and worked on pipes in my neighborhood and in front of my house. They send out plumbers to review the areas..end result, they didnt see anything wrong. A month later, I'm hit with a $735 bill! Why am I responsible for this bill? Now, the bill they sent me last year for putting food in the garbage disposal I paid, as they stated your not supposed to put food down the garbage disposal...kind of lost on why not, but I paid for it. Why am I now being responsible for any calls made now? I see this a a result of being pushed out. I could call on a lot of other problems, but all they are going to do is piece it together!