Help! Trying to leave Office Team

Sadly I didn't research enough about Office Team before signing with them, but they were all very nice so I don't have any big complaints... at least until now. I am currently placed with a company that wants to hire me full-time, but the agency is trying to push a large fine on them. Neither the company nor I have a contract with the agency and I'm not sure how to break away from them. I'm thinking of just not faxing them my hours and signing with the company, but I'd like some input of better ways to handle this. Thanks!