Pangu is stuck on my iPod, and now it randomly shuts off. Any help?

Awhile ago ago some kid stole my iPod saying he found it (not true) when I showed him the case I bought it in and got it back I reset all the memory. Even after doing this there was this Pangu app on it. I tried deleting it but it didnt let me. I looked into it and found out that it is a jail breaking app. I believe he jail role it wrong causing this app to be stuck on it. I also am having problems because it randomly restarts completely. (The apple symbol comes up) It restarts whenever I play games like clash of clans or goat simulator. It didn't do this before and is really annoying. Please help...