Unresponsive, frozen phone because of using "dummy file generator"

My phone used to freeze a little before but I downloaded an app called "dummy file generator" & the problem is almost gone. This morning I used my app but before I could delete all the dummy datas my phone got freeze & has been like that for a while. I tried taking the battery off & restarting phone but the phone is still frozen. what do I do now? Please help me :(