You entered into a contract with TalkTalk whereby they agree to provide a certain level of service in exchange for a fee. Provided you are getting the service they promised, then you can't escape the cancellation fee if you decide to break the contract.
If they happen to reveal your banking or other personal details to a third party, that isn't strictly speaking affecting your phone/internet/TV service. So as long as they continue to provide that, you are up a creek without a paddle if you decide you want to switch providers without charge.
TalkTalk may be liable to ensure you receive appropriate compensation if you can demonstrate a loss due to the data hack, but this will most likely be limited to refunding any actual physical loss of money from your accounts, plus interest. Nothing for the inconvenience or trouble.
I'm sure the cash for trash lawyers will be all over the media and cold calling for the next few months promising you an instant fortune - it ain't going to happen.