Can hackers exploit your iPhone through apps?

Last night I was playing the app "Party in my dorm" which i had installed 24 hours prior. Anyway some of the 'elite' players decided they wanted to use my account to trade, giving me a fortune in money, they insisted I upgrade to a certain level and join them. I wasn't interested in this because I don't have time to waste on an App, so i told them politely no, they seemed rather agitated by this so I decided i would delete the game.

However this morning my iPhone has been doing unusual things, it has crashed when i turned it on twice, which i've never seen it do once prior. Also somehow without my authorisation, PingChat connected to my facebook contact list and requested to be friends with one of my buddies

Now I'm well aware I am being paranoid, but it has all my bank details and credit card information on it. I am just curious could someone have gained access / still have access, and what should I do in this situation?