I'm going to keep this very short, my roommates moved another person into my bedroom, after I left for summer break and claims that they did not really move this person in, but their clothes are all over my bed. I am an illegal sublet, which I'm not legally bound between landlord-tenant laws. I'm a month-to-month tenant. After I found out this person moved into my room the following day I moved all of my things out of the house and proceeded to block all interactions (social media & cellular contact) from them so that they would not harass me for rent. They found out my e-mail and sent constant e-mails, started to berate me via social media and random numbers. They claim that they can still sue me in court for back rent, even though I was not on the lease, and all I signed was a fake document between me and the roommates saying I would pay x amount of money, but it's invalid, because written on it was "this is not the official lease, etc." What grounds do they have to sue me?