how would you deal if you are in a mental hospital and they dont want to let you out ?

I would probably take their advice and enjoy having a place to stay for now.  I hope things improve for you. 

I sort of deal with the same thing with my mom. She's in a nursing home and wants to live independently again. I personally don't think she'll ever be capable but feeling trapped makes her (understandably) feel angry and combative. I've found that setting goals and advocating for her helps. 

For example, right now, she's in acute care, meaning she needs a high level of assistance. She can't get out of bed alone, among other things. We've established the goal of getting her moved to traditional assisted living. To that end, it means she needs to be able to get in and out of bed alone and handle some of her own daily tasks. We have her set with physical therapy and occupational therapy and meet with her team to ensure they're supporting her. i.e. They need to be patient and try to let her do things while they're there to help rather than just jumping in and doing them for her because it's easier. On her end, she also needs to keep track of her physical therapy, make all appointments, and do specific exercises daily. In time, this should be enough to get her moved to assisted living, at which point, we'll talk to her about which goals she wants to accomplish next. 

Obviously, your goals are going to be way different than hers because she's got physical limitations, but you could always start by asking your care team what specific things are preventing you from living outside the facility and asking for goals you can work toward to demonstrate you're ready. For example, is there a way for you to earn money while you're there so you can demonstrate you can manage it and won't be homeless? If not, can you volunteer to gain work experience somehow? Just ideas... your care team can hopefully help you carve out a path that fits your needs and will make you feel like you're moving forward more.