So, I had this app called World Chef, it's a game and I wanted to start over. I deleted the app and then re-installed it. It didn't remove the data from the game so I deleted the app from Game Center too but the data was still there! I tried signing off from my account but that didn't work either. Is there anyway I can COMPLETELY remove the data from my device so I can start a new game? I also need the help with Game Center because the game is always in my Game Center and I think it is the cause of the problem.
I don't think Apple has a way to delete things or let you delete things - this is an iCloud general feature / design goal.
It's up to each developer to clean things (or ask you if you want things cleaned) when you delete the app or use the code in the app for resetting things.
You'll need to work directly with that vendor unless Apple makes a change going forward.